Power Rangers is such crap, I never understood the need to watch it while actual Sentai shows are available

In 2001?

Sure, nowadays we have access to 'actual' Sentai shows (which doesn't mean anything, because Sentai is a genre of tokusatsu, whereas Super Sentai is owned by Toei), but in 2001, 'actual' Sentai VHS tapes were hard to find.

Please expand on this part.

I've seen remarks which even frame Ultraman as a "Sentai Hero" and the only thing I can surmise is that "Sentai" has become a catch-all for "Tokusatsu Superheroes".

If so, how did this all happen!? Did Power Rangers put so much increased focus on the term "Sentai" that any Toku Hero is a "Sentai Hero" regardless of franchise or who owns what?

Sentai is indeed a genre (more precisely, a subgenre) of tokusatsu, but it has nothing to do with PR and was established back in the late 70s. The whole point is in the name. Sentai is a combat team in translation, so all team tokusatsu are usually called sentai. But neither Ultraman nor Kamen Rider in their pure form naturally belong to them. But Rescue Fire or Solbrain are.

Not really. Rescue Fire is a firefighting team with combat skills (and not even Toei) while Solbrain is categorized as Rescue Police within the Metal Hero series.

I'm not sure Toei has patented this term. Yes, in principle, if we go to the original meaning, which comes from imperial Japan, then sentai refers specifically to military formations. And then not even all Super Sentai are real Sentai. In principle, due to the vagueness of the term, we are talking about it now.

I don't know, I feel like the term is pretty set in what it is. I feel like people are only making it vague to bring about needless discussion.

Like guys we don't really need to get that pedantic about this.