One of the biggest offenders of this is Pillawag. Now, I also have no issue with some 10 stars designed purposefully not to be 'meta' or meant to fit easily in many builds. However, I think the tradeoff is that they should be interesting by themselves. They should be something to build around, rather than to fit in your build.
As it stands, Pillawag deletes special tiles and prevents new ones from spawning in a single 3 tile line in front of you. This is an absolute joke, honestly. This is a 10 star exclusive to a boss, but meanwhile you have weapons like Tarnada that was once metagame shaping, and is currently still quite strong that drops off a Jammer Delta.
Pillawag does not need to be at that level, but it could stand to be far more interesting. I'll give some examples/ideas of what I mean with weapons I think are the biggest offenders, including Pillawag.
- Pillawag: Could steal/claim enemy special tiles in a 3x3 or perhaps even 4x4 range in front of you. This would also be its attack range, and its scaling could remain at 85% as a tradeoff for such powerful utility and wide range.
- Jarmor: Gives you Jammer charges based on UL upon battle start. Every time you take a melee attack, you split off a jammer copy of yourself and reduce a charge. The copy has a fraction of your HP and stats and can be controlled or set automated like any other minion. Could give it either jammer alpha or omega skills, idk which is weaker.
- Leviathan Amulet: Change the resist into absorb since umbrellas exist and can get 2-3x as much resist in the same slot anyway. Also grants a skill called Sea Dragon's Roar. Absorbing water damage gives you X charges equal to the damage absorbed. You can use Sea Dragon's Roar to shoot out a line shaped beam of water that passes through enemies and damages all either equal to the damage absorbed or a portion of it, whichever is more balanced.
- Fox Paws: No big changes here, just grant it a skill that allows you to create a Seeker Flame (max of 1 active at a time) that has a LV equal to UL x 5 (max of 60.).
- Gigantys: On Miss: a 3x3 or so circular AoE around you that deals damage based off UL that maybe also knocks down. Keeps current effect in addition.
Now, there are other 10 stars that are definitely not up to par, but I think those can be fixed with number tweaks rather than reworks. I'm sure some of my ideas missed the mark either entirely or just a bit, but these are just meant to be examples of ways you can make these vendor bait 10 stars more interesting.