Honestly? Any Pokémon ban listed at facilities like Battle Tower and Battle Tree. There's no point in training them up unless you're just going to use them against the Elite 4, and it's not like you can battle other players in those places as far as I'm aware. There really is no point banning anything in PvCOM that isn't banned in PvP. Don't get me wrong, the major Legendaries and Mythical Pokémon are fun, but ultimately pointless once you've done most of the things in the game.
Kartana is really unsatisfying for me, becuase everyone can sweep wih this thing, but when I use it, it directly dies...
When I first read about Wimpod/Golisopod's ability, I thought it was fantastic. Once I get low on HP (probably because of an unfavorable type matchup), I can trade out for a more favorable Pokémon without wasting a turn? Well sign me up! In reality though, their ability is more of "get hit with a strong attack, and then turn that attack into a Circle Throw or Dragon Tail upgrade which doesn't have reduced priority". I would literally rather have an ability of "this Pokémon is always poisoned, except it can also be afflicted with other status conditions at the same time". I have never been so hyped and so let down by a Pokémon ever. If Gen 8 changes it so that Wimpod/Golisopod's ability instead causes the withdraw to happen after you get one last attack in regardless of your speed or if they gave it to some lightning-fast Pokémon, I would change my mind entirely. But until then: These horseshoe crabs are a great disappointment to me.
Dissatisfying, huh? Maybe some more useless Pokémon like the early bugs, Watchog, Unfezant, and Furret that you get early on but aren't good at all.
Box Legendaries and from the previous generations, HM slaves. Both types feel like pokémon that you need to progress in the game, but ultimately after a while they become kind of useless. I’ve also never really loved using legendaries or mythical pokémon because (and I know this is going to sound so pretentious) it feels like it takes away the whole mystery and special feeling around them. I’m not saying that we shouldn’t be able to capture legendaries in-game, but I think it feels more rare and special when I don’t use them. And housing them up in a PC box feels.a little wrong, in my opinion.
Luvdisc, tried using it once in a playthrough. Never again, it was just no. I don't really mind legends since well we actually have non-legends that are stronger than legends.
It'll sound weird, but I found using the Therian forme Kami trio in B2W2 quite unsatisfying. It was pretty cool to have them low-level at the start of the game, but they took forever to train and I eventually got bored of them.
Crabominable for me. I loved the heck out of Crabrawler, and it carried me through a lot of my Ultra Moon journey. However, after it evolved, it never seemed to do well. It was extremely unsatisfying to use, and honestly kind of a pain.
Drampa. It’s one of my favorite Pokémon in terms of design and Pokédex entries, but it’s practically useless in battle. Crazy high Special Attack and nothing else. It’s like the special Attack equivalent to Rampardos.
Any of the stronger legendaries. Feels like I'm cheating the game when I try using them. Oh, and middle-stage starters always feel dissatisfying to use, at least from my experiences (the only exception is Brionne). I usually want them to evolve as fast as possible and I never enjoy using them much in battle.
True Getting this small boi to lv. 39 is pretty hard, but evolving Zweilous to Hydreigon is much more annoying imo.