How many of those counterexamples are considered powerful? My guess is that you will only get 25 at best.
I understand your point though, as most characters do follow the same general flow, with the same general powers. However, with the presence of those powers and other already mentioned factors, it is hard to see things alternatively, where there is a large amount of variety.
They are all considered powerful, Eric. I'd like to see you do any of the things my counterexamples could do.
The examples you provide are OP. That is the difference.
And it really isn't difficult to imagine a world with some variety; we used to have it. It used to be a thing. If people were to realize that we can't all be the same thing over and over, and not everyone is fit to be a Madara after a single year of steady RP, we'd have that variety very easily.
I would impose the limitations as such, quite frankly.
Of the four maximum KG resets, you may claim two total in RP and must RP the acquisition of one of them. i.e. You are born a Kaguya, and must RP the acquisition of the Sharingan.
The KG resets are not limited to what they are; you can be creative with them, to an extent. Variety.
This is for KG only; things that are Hiden, for example, are still fair game methinks. A person could be knowledgable of a Hiden technique and still have KG, for example.
As for the other resets you do not claim; they could be used to claim other things, like large chakra capacity, or increased hearing, all of which must be acquired through RP.
I am spitballin' here, but you see where this is going.
The sannin (except maybe Oro) are not overpowered. in fact, the only truly overpowered shinobi in that list are current Madara, current Obito, and future Sasuke (we just know he gonna pop some circle eyes soon).
Hashirama - has one KG reset (wood release) and sage mode.
Tobirama- has Edo tensei, hiraishin, mastery of water release, that last one not really novel in SL terms.
Hiruzen - well, he hasn't been shown too much, but from what we've seen, he's got a variety of techniques in his arsenal.
Minato - Hiraishin and (weakly) sage mode. Let's be honest, he didn't have a lot going on, though he was good at using what he had.
Tsunade - Great medic and physical strength and endurance (cut in half, still trucking), but not the overpowered threshold..
Danzo - Izangi spam annoying, but manageable in a drawn out fight.
Naruto - 9-tailed fox, sage mode... That's pretty much it in the grand scheme of things.
Orochimaru - Sage mode, hiden technique knowledge, Edo tensei
Jiraiya - Technique knowledge, sage mode
Kabuto - A conglomeration of stuff, the true KG whore of the canon universe, closest thing to OP without hitting the top brass.
Nagato - Rinnegan. That's it. No Mokuton, no sharingan, just Six Paths. Not that bad in the scheme of things.