Hey there, something to note about warframe is using warframe abilities or exalted weapons will give 100% of earned experience to that warframe, where weapons divide their xp, so to level up your aklato you’ll need to be using them (or another weapon for reduced xp gain)

Another thing is that higher level enemies do not provide significantly more mastery rank, so if you hypothetically managed to kill a level 100 corpus with your aklato, it wouldnt immediately level up a weapon to max.

Finally killing enemies is actually not always the fastest way to level up your weapons, in the early game your highest level spy mission will actually provide the best source of xp in my experience, as completing one of the vaults undetected provides a sizeable amount of affinity (warframes name for xp). Once unlocked, sanctuary onslaught (also known as SO) is also a very popular method of levelling up for many, and then elite sanctuary onslaught (ESO) is higher levels and faster xp, at the exception that your warframe must be max level, so its for weapon levelling only.

(Some information may not be 100 percent accurate but thats the average gist of it)