So, after about 100 lock back empties, this is how my heat treated bolt catch looks like:
Pristine. It works.
Now the caveat; I no longer use the ping pong paddle to release the bolt. I always use the charging handle now and it actually is more efficient in reloading since I only have to use my right hand for the whole reload procedure (I am a left-handed shooter).
The reload procedure used to be:
right hand release mag
right hand dump pouch
right hand fresh mag
right hand load mag
right hand grip mag well
left hand slap ping pong paddle
left hand to grip
right hand to foregrip
ready.
Now the procedure is:
right hand release mag
right hand dump pouch
right hand fresh mag
right hand load mag
right hand charging handle
right hand foregrip
ready.
Mind you I have Magpul BAD lever that I removed on the WE m4 since it seems to cause enough weight resistance to not lock back sometimes on empty, so I removed it and am putting it on my GHK m4 instead, since the bolt catch on GHK / WA systems seems a lot better to me and more closely resembles a real AR bolt catch/release system.
Using the paddle will cause some wear, as I heat treated 2 catches. The first catch I attempted to heat treat I did not manage to get to correct heat treat temp and hardness, since it still notched the catch on lock back, but the one pictured I got nice and red, and is solid - there is no notching of any sort on lock back.
There aren't even any markings of the bolt carrier lip on the thing, I am quite amazed. Usually at the very least, there will be a tiny amount of notching every time the bolt carrier slams on the bolt release - in this case, there is no such wear.
I will be doing this every time I need a new catch, which will seem to be a lot less now since I can't get catch to wear/deform yet.