...and? What if this miner found this block first by timestamp, but some miners on the network refuse to build on it, and nodes refuse to relay it, due to its size? If there is no hard consensus rule, what is to stop miners and nodes setting local policies that reject blocks beyond certain criteria? In that case, how will they remain a network?
No, you fundamentally misunderstand how bitcoin works. Orphaning only accounts for the latency issues around relaying blocks to the network. It doesn't address the idea that nodes and miners may refuse to relay blocks beyond a certain size. If so, and some miners continue building on such blocks, we see chain forks. Likely we would have many, many forked ledgers instead of a single global ledger.
That are big misconceptions, no rational miner is going to continue working on smaller chain, because longest chain = Bitcoin. Even today there can be many forked ledgers (miners building on top of smaller chains), but there is little reason to do it thats why you dont see it today and wont see it in future when the hard limit is removed (it is beter to stop wasting electricity if you cant build on top of longest chain, unless you do some experimental pet project and dont care you mine worthless blocks others ignore).
Miners may refuse to relay blocks beyond a certain size, the same way as today they may refuse to build on top of block of certain block version number or any other reason they choose like included transaction with blacklisted coins. They dont do it because of selfish financial interest to be on longest chain + Bitcoin price