Gifted is +3 mellee skill, +3 def, +4 fatigue usualy (10 stat total). Or +4 range skill/def, +4 fatigue for rangers (11 stat).
Shield Mastery is +3.75 mellee def on round/kite shields and +5 on triangle ones. A bit more than 3, but no +fatigue, skill etc. But realy helps vs axes and also boost range def (+3.75/+6.25).
Fast adapt is +8 skill after miss. If your chances is like ~50% it usualy means you will gain 8 skill on every 2nd attack, so it’s like +4 average on every attack. But no fatigue or def. Great to deal with perseption skilled ones.
And you can take these perks both for boost low quality merc.
Anyway gift is good even on some undertalented characters with great base or on nice talented, but low starting stats.
Maybe making talented to up 4th stat as well will make it better but not OP (resolve/initia/gibrid attack skill etc/2nd def or hp for tanks).