Fast adaptation requires to miss a hit to stack up. With two hits only per turn, it puts off its benefit to the next turn. Which can not be afforded.
Beside, characters are converging toward 95 pc. If the character can make it late game, it appears to be useless sooner than later.
It is better to use spears when a character starts on the low side of the hitting stat instead of this perk as spears give a 20 pc increase on all hits
Three perks are said to be mandatory: scholar, steel brow and battle forged.
The others corespond to four builds or are used to correct a deficiency in a character.
For example, the minimum of resolve to achieve is around 50. If a character has the proper starting stats to fit one of the four builds but is weak in resolve (like 25)
perk to boost resolve is applied.
You don't need steel brow for your tanks you need them for your archers. You don't need scholar for anyone except if you want to lvl them faster. They will have 1 less battle perk until lvl 11 if you take scholar. Battle forged is not needed for your archers. So you need to watch some more videos