what type of PA?
feedforward double loop PAs are well-known and popular, but still hard to tune and get it right the first time..
digital predistortion is not easy also, since it is relatively new method..
In short, linearizing a PA is hard..
or maybe you meant just circuit level, like matching ...etc. that is relatively not that hard, just spend a couple of days twieeking ...etc.
I am not sure did I understand you correctly, or if I answered your question...
Cheers...