This is either a bot comment, or you have a very poor understanding of the UK financial market. They are quite far down the leaderboard for ISA rates and SIPPs.
The parent comment didn't mention anything about ISA rates and SIPPs in terms of performance, they said that it was easy. You might disagree with their priorities but that doesn't change whether it's the right decision given those priorities
While Monzo are expensive their approach of rewarding loyalty (5% off per year for Monzo Mobile) is a good idea compared to the endless switching you have to do to get the best rates.
I don't think they actually are. Platform fees are capped at £250 and their default managed fund fees is 0.14% which is pretty normal. Also I deliberately want a platform that doesn't allow trading individual shares because otherwise I have to report those to my employer every quarter and I can't be bothered with that admin.