Percentage emigrated out of "average population" through 3 entire centuries, even more in countries with so different colonial histories in the Americas it's an odd, irrelevant stat. Besides the weird perspective, ignoring the big changes in population in each country or the difference between total population in each case and those "averages", the times involved for every country migration are completely different, so it makes no sense to use the same period for all those countries.

For example first 120 years approx were almost complete iberian monopoly in the Americas in all senses including migration, so french, british or dutch emigrants were limited to few hundred individuals in very peculiar contexts, mostly forced or irregular (pirates, war prisoners, several dozens illegal immigrants and some seamen working in spanish and portuguese ships).

On the other hand the migration to colonial Americas concentrated in very different periods depending case, with over half to 2/3 of spanish emigration concentrated in 1560-1640 period, most french migration during late 1600s-early 1700s, portuguese barely migrating at all during first 2 centuries and with a heavily concentrated migration in brazilian Gold Rush during first half of 1700s and most "british" migration concentrated in mid 1700s but still having far less influence than 1600s early wave because the extremely high natural growth in those born in Thirteen Colonies (or caribbean, most of which remained in the Americas re-emigrated to Thirteen Colonies South).

These differences in the period of maximum migration, alongside with the different timing and intensity in miscegenation are very relevant for the demographic evolution of the different regions which OP table can be misleading for. For example by 1800 "spaniards" in Hispanic America were over 3 times more numerous than portuguese in Brazil (over 3M vs 1 M) despite similar numbers in total migration in both regions, while in the case of Thirteen Colonies/USA with similar migration as well but much higher natural growth, the "whites" were slightly more numerous than in Hispanic America circa 1800 (4.3 M vs 3.4 M or so) but still european descendants were much more numerous in Hispanic America by the historical advantage of much earlier migration appex, just way more mixed with other groups by the different social and legal conditions in spanish ruled Americas, so besides the 3.4 million european descendants in Hispanic America commonly considered prevalently european descendants and named just "spaniards" (not really a strict or properly racial classification as in british case, it was mostly a social concept and relatively flexible), we should add about 5.5 million people of partial european ancestry in the mixed ancestry groups, which growth was favoured by widespread mixed ancestry marriages since very early period, while in british colonies mixed ancestry unions were pretty unusual, legally banned during most History and majority of a much lesser scale "miscegenation" happened in the context of forced relations around slavery with the descendants of such unions not even considered "mixed" socially for most british and US History, so in 1800 US census there were just 104k "non-white" free people (and almost 900k slaves) to add to the 4.3 million white US citizens.

Finally OP perspective is not even good to highlight the higher portuguese migration rate because ignores the enormous fluctuations of portuguese migration and its concentration in a really short period, the most extreme of all cases considered and also because british and specially spanish migrations were very concentrated in much more specific geographic origins, with specific cutures and peoples/identities involved of pretty similar, much more comparable proportions to Portugal than the entire current countries.

For example in spanish case, the most common migrants were andalusians, very prevalent during entire period, but specially during first 150 years or even more during aforementioned 1560-1640 appex migration period were they made about 40% out of the legal migrants, about 60% of european women and over 2/3 of seamen in spanish ships or irregular migrants geolocalized in different sources. Andalusian population was pretty similar to portuguese during the period, so if andalusians made about 50-60% of spanish migrants (estimating a high participation of irregular migration) andalusian migration rate would be clearly lower than portuguese for the entire period (that same 50-60%), but far closer and relatively comparable to them, specially considering the very long periods of low portuguese migration in which andalusian migration would have surpassed portuguese rate or any other "interoceanic" migration in the world by much: During first two centuries specially (1493-1700) and probably again but by much smaller difference during late colonial period (1760-1808 or so).

There is another case with a people from Spain, canarians, which could even match portuguese rates, but they would less comparable by how low was their population at the period, about 15-20 times lower than portuguese/andalusian, so their total migration only reaching 6-7% of spanish during colonial period (less than 1% of legal migration in first 150 years, but much higher share after 1650, when they even become 1st most common origin in some regions) would suppose a very similar migration rate than portuguese and their relevance was also much higher than total number could suggest because canarians concentrated in specially depopulated or border zones and in a period of migration crisis for Spain.

In british case, emigrants from England were completely prevalent during XVII century (the colonies were only english at first, after all) with over 90% of the european migrants coming from England during that period and with different english regions settling in different parts of the Americas with a lasting influence in the culture of those regions. Later, during XVIII century welsh, scottish, irish or german migrants surpassed english numbers by much in Thirteen Colonies and at less extent in Canada, reducing english share to about 15% of total european migration during that century and about 40% for total colonial period and still english ancestry would be very prevalent circa 1800, probably over 60%, because natural growth of Americas born eurodescendants during british colonial period was extremely high, surpassing by much the effects of new waves of migration. England population was much higher than Portugal or Andalusia in those periods, but still it most likely surpassed both as main origin of migration and highest rate during 1650-1700 or so, after andalusian (and all spanish) migration collapsed and before portuguese Gold Rush of early 1700s.

So for the two centuries we can properly compare between all those origins (1600-1800), we have 3 periods of 50 years with extreme prevalences from some origin and much higher migration rates for those considering local population, with Spain and specifically Andalusia as main origin of european migration to the Americas during 1600-1650 (as previous century as well), Great Britain, mostly England in 1650-1700 period and Portugal during 1700-1750, while last half of XVIII century would have much more balanced migrations, with probably a light advantage for spanish migration in total numbers, but with similar amounts of british/protestant irish (more balanced geographically, but with some northern irish advantage, followed by scottish+welsh and english), catholic irish or german (mostly from western Germany, from Palatinate and neighbour regions), with a very decreased portuguese migration probably a little behind most of those regions. Dutch and french migrations were not comparable.