Anyway, you'd need a large capital to account for the rich.
There isn't such thing as decentralized where all the infrastructure and trust is under one owner(s) which is the case with all I've seen. Multiple trusted parties makes corruption easier. Both increase attack surface and cost-overhead which would be passed on to users.
I also have high-doubts most tumblers to date actually covered in the beginning. I even remember some with a lot of users having trouble with rollover.
Bitmixer.io, BitLaunder.com, Coinmixer.net aren't decentralized and the only obfuscation they have is internal input tagging; all considered the top mixers. Mine does second-level splitting of inputs before it even uses them for mixing and has PCIe hardware isolation of private keys.
There was one mixer once that did what I do but didn't have hardware isolation. I think they were killed by rollover. I forget the name.