I would NOT leave an extravagant tip for nominal service! (I understand guilt requiring you to leave a tip, I probably would too.). I would also request a different butler and personally, I don’t think you have to give a reason. It should be obvious. It could be this particular butler is being monopolized by one suite, but it is his responsibility to divide his time equitably among his suites. He can decide which suites to shortchange. You paid for the services of a butler (I know they are called something else, but even our ‘Retreat Host’ on our last cruise called himself a butler) just as any other suite guest and it doesn’t sound like you have unrealistic expectations.
We were lucky on our March Apex cruise (CS) when we had a wonderful butler. He ask what we would like brought every afternoon (cheese and crackers rotated with shrimp cocktail) which he brought promptly at 4:30 each day. When he realized we would return to the room about 4:45/5:00 each day with a glass of wine, he started bringing the wine as well, eventually bringing a bottle of my favorite ship Chardonnay. If he saw us anywhere on the ship he made an extra effort to make sure he spoke to us (sometimes at length-he was a talker!). He could not have been more helpful.