The weird thing is that I don't think Lighting centralizes anything at all.
All it does is provide a way for 2 people to send BTC back and forth off chain.
It's intrinsically very decentralized and permissionless given two consenting parties.

The real thing centralizing Bitcoin is the refusal to increase the blocksize to match technological inflation. That shit is rolling down hill into Lightning with the expectation that Lightning will fix it, even though it can't.

It's also interesting that you mention XMR... because I'm not sure that XMR is any more scalable than BTC is. In fact logic would dictate that zero-knowledge proofs are a lot of extra steps so it may even be less scalable. We won't know for sure until people are actually using it. Serai DEX could be the breakthrough everyone has been waiting for.