As far as I understand rollups are scams. The optimistic rollup arbitrum had to throw towel in the ring a few weeks ago when fees became higher than on ethereum. They stopped the event they were doing. Arbitrum is a PoA rollup so there is no consensus mechanism. Arbitrum gets all the fees and decide which transactions to include or not. Despite this centralization they still ended up with fees higher than base layer. They are working on optimizations but that's it.

Zkrollups can perhaps do 5x more transactions than optimistic rollups before the ceiling is hit. But it's next to nothing when you want to do everything in a blockchain manner and want millions of users but i could be wrong.