As premined coins hit the marketplace, it's the market that determines the price, not the original miner.  So yes, the original miner could try to sell coins for more than the market price, but depending on his asking price, he might not be very successful.

I agree with you that the mining of PoW coins becomes more centralized with time ... but this also means that by default, the processing of transactions also becomes more centralized.  That's the problem you've been seeing with Bitcoin for the past months - transactions are now taking hours to process, unless you're willing to pay a higher fee.

I don't think anyone is saying BTC is all bad, but there are a few significant well-known issues that need to be addressed or the coin will eventually fail.