My take on this is that it's similar to how perhaps the guys who got into metal in ~78 felt when they heard Morbid Angel and Deicide. Some of them liked it, most of them didn't. I recall a funny rant by Bruce Dickinson in the 90s (may have been early 00s) about how he didn't understand the subgenres of metal. He had no connection to it, didn't enjoy it and didn't see any distinction in the bands.
I got into metal nearly 10 years ago and you could easily call me a 'true' guy up until last year. I still really dig a lot of the core bands. Point is I see The Acacia Strain being to Whitechapel as Slayer is to Megadeth - Same genre, same playing techniques, same general production. Different feel, subtleties and such.
There is hope yet. Djenty stuff is taking off at the moment. That will likely bubble up and everyone will hop on that bandwagon. It's just how it goes. Two years ago I was listening to City by SYL and thinking 'metal hasn't come any further since 1995'. Since then I've found out about Djent, Deathcore, Modern Death Metal (and Tech Death, which has exploded into a genre with stylistic elements unique to it recently).
Metal will continue to grow, and as engineers we will have to record a lot of generic bands. That's just part of the job - the evolution of heavy music will go on. If you weren't doing core bands, there are a lot of other genres that are just as samey with hordes of bands that you would be doing to make your living. At least you aren't doing bar bands!
