That's a stretch given the context. A smart TV maker can put whatever they want in their own client software. They don't care what features Firefox and Google support.
They could also do that with out DoH, they dont because it is not "trivial" and prone to all kinds of downsides.
DoH is the problem here, as it hides things from network operators making it harder to block ads, spam, and other items at the network level under the guise of privacy, when in reality DoH's actual goal is to further centralize the internet into approved gate keepers like CloudFlare and Google.
I would rather pay more for a TV than have it subsidized by ads. Or even better, a TV with no smart features, then I can just connect a computer for whatever smarts I want.