I play in a mostly covers classic rock (with some soul / groove) group. Currently it's 2 guitars, bass (we all sing), and drums. We are all very experienced (thousands of shows played each) and pretty good at what we do individually, and as a band. We don't really have an official band leader, but I'm certainly the low man on the totem pole as I've found out when trying to negotiate our stage setup so I can stand next to the drummer and having been shot down categorically with no good reason given... The other 3 guys have known / played with each other for a long time and I've "only" known the guitarist for 7 years... That having been said it's a good group of guys, we communicate well for the most part, and we're friends.
So I go away for a few weeks, and I'm told there is a keyboard player coming on board, which we've talked about before. Great! I'm psyched. They jammed with him a couple of times while I was away. We schedule a rehearsal when I'm back. I meet the keyboard player, he's cool, nice guy. He has performance experience, but he's never played in a band before. He's a piano player, not a keyboard player. He's doing block chords with two octaves on the left hand the whole time. We all have pro gear and he's got a cheap yamaha keyboard which has no decent rhodes, wurly, or hammond sounds, he hasn't learned any of the actual keyboard parts for the covers.
So after the jam, one of the guys asks me what I think, and I more or less tell him--nice guy, has some talent, but is not a "keyboard player" and needs a lot of work before he would be gig ready with us. But at the same time I conceded that there are no experienced players with nord electros knocking on our door. He more or less agreed. I text one of the other guys (who was telling this "keyboard" player how good he sounded after the rehearsal) and let him know my issues, that I don't think he's a good fit. No response.
The goal for this band is to play a few local / regional gigs a month (for money), and to sound professional. I play in another band already so my "play music" fix is covered... So, what would you do in this situation?
I am in the same situation with regard to a piano player. (We all formed the group together so remove the band politics from my situation.)
You just have two choices.
1) You have a conversation with the keys guy. You ask him if throwing some organ and synth stuff in is even an option. You explain to him that his left hand will be cut off if he can't learn how to not play bass with it. (Laugh after you say that so everyone think you're kidding.... even though you're not.)
2) You just became a piano band. Stick to Skynard, Michael McDonald era Doobies (Takin It To the Streets is a JAM!), and stuff like that.
But you HAVE to explain to the band that there will be a sonic CLASH if he can't reel in his left hand. If the piano is banging away on a root C, and you start playing passing tones in the same octave working up to the IV it will sound HORRENDOUS out front.
There's a huge difference between an A9 chord and an Asus2 that occurs because he's playing the low B in the same octave you're playing the low A. YUCK! In middle and high octaves, a sus2 can sound great and add tension. If the A and B are both in a lower octave, it gets ugly. And there's no way to discuss every instance where that stuff can happen.
All are bound by the laws of physics. Sound waves are simply physics in action.
We are morphing from 2 to 1. What I mean by that is piano is our guy's forte'. But he's trying to become a synth/organ guy. We started with primarily piano songs and have been able to pick up about 10 or 12 good organ and synth songs. But his ego is in check. And we're all realistic with our expectations as well as appreciative of his efforts to step outside his comfort zone. It's cing together well.
Best of luck with your situation.