Is it not obvious that sets with a set bonus would outlive their usefulness as any other gear. I don't think it should be complicated and be getting massive stat boosts at all.

Using the i90 example. That gear should, as at whole set, be no better than i115 imo. If nothing else it just adds another level of accessibility to people and options to those that want them

There's merit in making gear statisticly desirable but the set bonus would make that big of a difference.

For another example. Let's say that we have a full set of i230 gear with a set bonus that is statisticly equivalent to I 245 gear bit slightly better stat wise, or i260 being as good as i275 gear and slightly better.

The bonus shouldn't be so crazy that it would be relevant much later in content

I've seen in some mmos that have a set bonus, give the player some kind of cosmetic particle effect that is somewhat unintuitive but noticeable.