The only way you could positively claim the engine compression was low is by running a compression test.
Which I doubt was performed.
Nevertheless to answer your question
in the overhauling process mechanics seem to do a couple of things ( wrong )
a. play with the cam
b. trim the big ends
c. try facing the cylinder walls.
Now,
There isn't a workshop equipped to trim or polish either the overhead cam or the big ends properly that I have seen ( and I have seen a LOT).
Once the timing cam is adjusted wrong, there is no life !
Secondly most importantly, the cylinder walls are made of a special alloy that compensates for expansion and can withstand
continued stress.
What the mechanics do is that they try to face the cylinder walls or insert cheap sleeves both of which destroy the capability to maintain compression.
What is more, they will use abrasives to face the cylinder walls without going through the honing exercise.
Thus, my suggestion:
a. It is not always that low power is due to worn out engine, some times other things can fix the problem.
b. Should you need to overhaul, just buy new pistons and insert new rings on them. Same size. don't play with the engine block.
c. Pay attention to engine head and seal; don't play with valve stem seals, and do not let them play with cam shaft.