Floor 6? Must have met Polette archers then. A very neat enemy indeed. Strong resistances too
You can always check the Wikia for those.
Can try to Sleep or Confuse them, but must be quite lucky, as they have 75% resist (and chances scale depending on your and enemy level)
Wait till you meet mobs of their big sisters, Stargazers, later on though
Actually weaker Resistances but the rest... Just wait :D
Also regarding Summoners, I think you're approaching it wrong. First of all, enemies with 90% Resist are difficult AF to capture. Try some 80% maybe (like Nue from the vulcano if you like Samurai monster adventurers... or Tempest Efreet from Hastrana Air Caves if you like Brawler monster adventurers... or maybe the Minotaur from the first post-game dungeon.. think he had some crazy HP regen values).
The listed resistance % is for a single roll. Enemies get a minimum of 2 consecutive rolls, often 3 or even 4 (depending on Summoner's level vs their level). In principle for enemies with 80% or more resistance you preferably want your summoner to be higher level then the monster he tries to capture (was it 7 levels above? or maybe 5? not sure anymore - when they get only 2 rolls). 50% and below ones are fair game regardless of level, though.
It's
possible to capture high level monsters with high resists, but it usually involves Brawler combo sheningans (successful full combo lowers resist by 20 - for the next action ONLY), setting up party order and hours or days of reloading and re-trying.
Gaia, one of last Floor Bosses from base game is nice target practice if you want to try that - actually doable even without a Brawler (you can reliably CC him and you can actually outlevel him in early post-game). He basically carried my party trough half of the Tower. Tower enemies you'd potentially want to capture are usually really difficult to keep under hard CC lockdown.