Question about Proposer Builder Separation

Hi guys, I am needing help from you Ethereum big brains out there as I am still trying to wrap my head around the implications of PBS.

There has been much discussion about PBS causing potential censorship, but I am interested in how this mechanism plays out long term. I assume that over time more relays will appear. How do node operators control which relays they use? Will they even be able to tell what exactly the relays do? And should this be the job of operators to judge relays?

Putting block generation in their hands means they get a lot of power. Is it possible for a relay to just "buy" entire blocks on the chain monopolizing it for a short time?

Example: let's say there is a very time-critical opportunity like a highly anticipated NFT drop etc - could a relay decide to put up a high bid on just a bulk order of said NFT and crowd everyone else out?

Or, say, there is a massive gas spike. Could there be a situation where a relay could outbid others for several blocks in a row, slide in a few empty block to force gas down and then send their own transactions, potentially net saving gas fees by leveraging their monopoly?

What are the implications? Other bad scenarios? Thoughts? Looking forward to your input.