Most games end before they get to high levels for various reasons, including the fact that WOTC doesn't publish modules for high levels because, wait for it, most games end before they get to high levels.I don't want to repeat the same things again and create another one of those topics.
But the statement I've said has been said numerous times on social media and other forums. The "it's only here" thing is a myth.
Now if you are staying their is a Massive Online Bubble, you might have something. But it's big
Whether it's an issue for other people that want to play high level games and are willing to run homebrew campaigns? I have no idea how widespread it is and neither do you.
It hasn't been an issue for me. In 3E the game absolutely had an issue with linear fighters, quadratic wizards. In 4E the game slowed to a crawl. There is simply nothing inherently broken that can't be resolved if the group wants to make it work in 5E. The proof? I, and others, have done it and it works well with minimal or no changes to the rules.