So am I to understand that if I own a 3700X but want to watch Peacock I have to toss my current device that I already paid for and buy a newer Roku? Anyone else think this is an issue?
Well, I haven't yet looked at Peacock, and I don’t have a 3700X, so it's not an issue for me, but if it is an issue for you, you might want to contact them (Peacock/NBC) and ask their developers to try harder to support the older platforms.
As for having new software not work on old platforms. Yeah, that's the world of technology. I still have my first personal computer from 1976 - but only as a memento. Absolutely nothing modern runs on it! In between that and my current computer I've tossed many because they were too old to be useful, yet too new to be "collectible".
As noted, this is a decision by NBC/Universal to limit their support to newer devices. Looking at hardware specs, all of the supported ones appear to use ARM-based processors. The other devices use older CPU's that work very differently.