...I think if you removed spinstab from polearms but let them keep polestagger it would be fine.
Polestagger - an uncontrollable mechanic that causes a player to lose control of their character longer than normal for a melee hit, enabled on nearly every polearm with few exceptions (those without knockdown) without any thought put into how it will change the balance of those items.
Spinstab - a technique that allows certain weapons to land hits when they would otherwise glance.
Notice the word "technique" in reference to the spinstab, you actually have to do something actively to use it. Polestagger was a 50/50 chance on any melee hit with a weapon it applied to. Random mechanics tend to be hardest to balance, and ones that cause you to lose control of your character are extremely not fun for their victims. The fact that this one in particular was
so widespread and used by so many items which could only be taken advantage of by one character build was patently unfair. The fact that the chance for it to trigger was so high is just absurd.
I feel the opposite way you do, Huey. I feel that spinstab should be allowed to stay (at least to an extent) because it's something you can learn which enriches your melee combat. Polestagger was a random ruination of other peoples' fun which they (or you for that matter) could have no control of.
Now, of course, spinstab still has its issues. I don't feel you should ever be able to swing twice and succeed if the other person blocked your first attack, assuming they start attacking, unless there are extreme circumstances involved (they're using a much slower weapon than you, teamplay/not 1on1, glancing on walls), but that also applies to hiltslash and I guess crushthrough. Blocking then jumping and turning into a person and landing a hit after you've just dinged against somebody's block is ridiculous. Stabbing through teammates is ridiculous. Stabbing over and around walls is usually ridiculous.
What's not ridiculous is using a spin to land a hit on someone just because they're close to you and your weapon is over 150 length (within reason). This mechanic can be stopped so easily, you just have to watch for it and block down. It's a problem when you don't block it, but I will say that it's highly exacerbated by the immediacy of the active hitbox. Spinning to decrease the time between the start of your swing and the time you can viably hit someone with it is bad, but you should not be helpless when someone is in your face just because you chose a weapon that only has two attack directions.
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DisclaimerI haven't been on servers where the spinstab nerf was enabled. I do know that I do a lot of last minute corrections during the attack animation on every thrust I put forth, mostly to avoid teammates with them. The speed at which I can turn will greatly affect the amount of times I can viably thrust without teamhitting. So, that'd be a nerf for teamplay as well.
As for polestagger, I don't think polearms players are that bad off without it.