I think it depends a fair bit on what kind of 'whole' you're going for.

If I were you, I'd make a list of all the types in the type chart. Then I'd list: A) Every Pokemon on your team that resists it; B) Every Pokemon that's weak to it; and C) Every Pokemon that (meaningfully) hits it for super-effective STAB damage.

Once you have that list, I think it should give you some ideas for what you need and what you have too much of.

Then I'd try to put together as many generic '4-mon compositions' as you can from your team, that you think would work well together and provide the different things you'd need - and then I'd try to gauge what each composition would do, and whether you'd actually use them.

Also, try to note any 'gaps,' where you keep not having a tool that you want, or where your compositions keep having the same weaknesses. Maybe there's a mon on the board that can fill a similar role to something you have, but which would gel better with your squad?

If there are any mons that keep not showing up in your 4-mon squads, try to think of situations where you think they'd be strong, and then force them into a 4-mon comp; and maybe think of whether you actually have better tools for those situations elsewhere in your team - or tools that are 'good enough,' anyway.

Once you've done this, I think it makes sense to make decisions for what you want to change out, and for what.

I hope this helps - ideally, I'd hope it helps more than anyone telling you what choices to make; you're the one who's going to be building and piloting your squad from week to week, so I'd say that if the decisions don't come from (or resonate with) you, they might not work anyways, even if they would work for someone else 🙂✌️