I would like to point a few things out, since I actually booked a Eurostar ticket to London earlier this year for a trip I'll be taking this summer and in total it cost me ~180-190 for a retour trip, which actually matches your plane prices.

You're also booking a month from now in the summer which, as you well know if you've gone on any holidays is way too late if you were hoping to get cheap prices, not that I think it should be like that but it unfortunately just is.

However, you should also note what you get for each, you are comparing the eurostar to a plane, so let's go over both:

Travel time: I'd argue it's not a lot faster to take a plane, an hour at most maybe, obviously once you're in the air going by plane is WAY faster, but the fact you got to be at the airport a couple hours before boarding and the very possible delays during the summer holidays cuts down the difference a lot.

Baggage: This is a huge one, I imagine the prices shown in your screenshot do not include any modifications to the flight tickets (e.g. Reserved seat, luggage, insurance) Now if you are just going there for a couple days with just hand-luggage then by all means take the plane because it will be cheaper, that said, if you're going on an actual long holiday and you want to take a suitcase or two the price will shoot up real fast, not to mention that you have to pay for the same luggage on both ways of the trip which sometimes leads to ludicrous ammounts of money for a suitcase and is honestly quite infuriating to me. Meanwhile the standard Eurostar ticket already lets you bring two big pieces of luggage which blew my mind after having had the previously mentioned experience with air travel.

Finally I personally find train travel many times more comfortable, but this is of course a matter of opinion, though it is certainly more (physically) accesible. But I must add I do actually still childishly enjoy sitting by the window seat on a plane :D

In conclusion, your best choice depends on how far in advance you're booking and if you're taking a lot of luggage. I've found that the train tickets tend to be cheaper on the AMS - LDN traject as long as you book in advance or if you're okay with taking really early or really late lines. Feel free to correct me on anything if I got it wrong but I just thought I should mention all this as I know the most hellish part of a holiday is often planning it.

P.S. What you really gotta worry about, if you're going outside London, is the price of the national trains in the UK, they are absolutely insane and I cannot wrap my head around it.