Yea, I hear You.

I haven't run the stock for a long time; they are adequate (at best) for a stock setup heli, but performance deteriates fast with added weight or more powerful motors that You are describing.

I think the E-Flite batteries are of good quality and have longevity, but if they are going to offer upgrades, a battery should be among them. I think they messed up there.

My heli is at 241 Grams compared to a stock set up at 227 Grams, so the 15c batteries perform pretty good, but I fly almost exclusively the 22c's from SMC now, and my heli feels lighter than stock with those and can get the full 9 1/2 minutes with them.
The 180's seem to love them, don't get very warm at all.