I'm pretty forgiving when it comes to setups for kicked-out-of-the-party manga, but this one's is a bit too mind-meltingly stupid. In others if I see something like... The party was just using the protag and always planned to betray him. Fine. The party thinks the protag is weak and holding them back. Fine. The party leader just wants to bang protag's girl so they kick him out. Fine. There's a billion extremely simple reasons I can accept.
Then there's this one. "Oh, you're just distracting the monsters and taking all the hits for us? UMMM how STUPID. Our party is an OFFENSE-focused party, okay? It's kinda our thing, and you're all up there with your insane deeeeefense. Boooring. You're really ruining our whole THEME here, so y'know, go pound sand or whatever." Like... They KNOW he's strong, they KNOW he's useful. I get that they're trying to portray them as arrogant as not NEEDING to rely on his defense, but it doesn't feel that way at all. They're just cripplingly retarded. They even mention how no monster can stand in front of them for more than ten minutes. You need upwards of TEN MINUTES to kill a monster, even while you are able to focus purely on your offense due to that one guy. Yeah, I'm thinking you might want SOMEONE up there to keep its attention for you while you're all whacking away at it for minutes and minutes and minutes, just in case. And who knows when you might encounter something unexpectedly stronger too.
And they of course IMMEDIATELY run into problems. "Oh hey, that guy we adventured with for so long, who would always draw all the attention from the monsters and allowing us to use our offensive abilities freely. He was pretty useful, huh?" Yes??? Did you not realize this as you were fighting in all those prior instances? Are you seriously that unaware of your surroundings? Were you blacked out? Were you in a coma? Like... What? They're now constantly failing missions. Background characters are gossiping about them and how it must be because they kicked that one guy out, and... Yeah. Yeah it is. Gee, that sure was a brain-dead decision wasn't it? It's so painfully retarded, I can't handle it.
I don't tend to pick apart logic in these series, but it's just such a glaringly dumb, flawed premise that didn't have to be written this way at all. I need to give my brain time to recover before I attempt this one again.