Very large ETH miner here, we use GPUs. Mostly 4-5 year old tech too. Unlike BTC, ETH does not require the latest hardware because the algo, ethash, is memory bound. This is a great explainer [1].
You may be implying that the majority of the network is custom ASICs. I doubt it is more than about 30%, if that. Come august, all the ones with 5gb of ram will also disappear off the network because of DAG growth.
GPUs are also not destroyed by using them. I've got GPUs sitting in the worst possible conditions, running just fine for many years now. We have started to change the thermal paste on the hot ones though... it dries out. I don't know what you were dealing with, but that sounds like something else caused the failures as the chips themselves don't wear out like that.
[1] https://www.vijaypradeep.com/blog/2017-04-28-ethereums-memor...