I feel like the amount of ads and/or length is a little excess these days, though.

I do agree but their costs have also skyrocketed because the resolution and frame rate of videos has skyrocketed.

Linus Tech Tips did a video about this ... which agree with his conclusions or not, he paints a clear picture about how YouTube is more expensive to run than it used to be https://youtu.be/MDsJJRNXjYI

Google also isn't in the business of "running things at a loss in hopes of future profit" anymore ... so they need YouTube to be profitable. Maybe it's "too profitable", maybe they could cut down on the amount of advertising they use ... but you're absolutely right that they do test this stuff and find the threshold between "annoying but profitable" and "annoying but we're losing users."

More competition is always good ... but Google isn't stopping competition from showing up, just like Valve isn't stopping competition from showing up, they're just providing a better service that creators keep coming back to (because it's ultimately good for those same creators to get their content out there and monetize it).