Alright here's what I found
There are a lot of things used by the AI that, well, aren't the best. While listing even single one would be impossible, I have gathered most of the items used in gen 7 battle tree that aren't as good as others. Note that this is a bit biased cause I found it. But I'll give you this google sheets to see for yourself. Make a copy if you want to use it for yourself. Also, I likely missed a few, but don't judge there was a lot lol. Alright here goes.
Super effective damage lowering berries.(they used pretty much all of them)
Type move boosting items (charcoal, magnet, mystic water, etc.)
Bright powder
Kings rock(this is good on things like cloyster and cinccino, but they weren't used on them)
Lax incense
Wise glasses
Big root
Focus band
Shell bell
Float stone
Quick claw(not bad, but not the best)
Status condition curing berries(paralyisis one especially. Lum and chesto are actually not bad)
Absorb bulb
Muscle band
Wide lens
Razor claw
Razor fang
Wise glasses
Scope lens
Zoom lens
Jabboca berry
Binding band
Cell battery
Luminous moss
Like I said, probably missed some, and you may think some of those are useful, but also like I said, there's the Google sheets if ya want it.
Hope I helped
EDIT: I found the original page I found the lookup on I think, so here is the link. You open the sheets, make a copy, and then you can use it for yourself an dit should work. If it doesnt, I'll try and find another link.
