It’s not really a technical problem anymore. Which isn’t to say it’s easy to run such a site, but rather to stress that YouTube is like a social media site. The value is in the users (and the content that they create and consume). You could make a perfect YouTube clone, but good luck getting people to use it when their favourite creators don’t. And good luck getting creators to care when the users aren’t there.
And Lemmy is misleading. Most people don’t use Firefox. Heck, most people don’t seem to even use ad blockers.
The captions suck too. I subscribed to the same deal as you. I did it mostly to support the creators. But I basically never use it. The creator whose affiliate link I used to sign up? Their own captions are amazing on YouTube (human written with colour and positioning) and auto generated garbage on Nebula.