They might not directly change consensus rules but their behaviour and communication paints a clear picture of "use our software, follow our rules or you don't use Bitcoin".

That kind of attitude makes policy rules balance at the edge of becoming consensus rules.

Their (core) arguments have been many, from unifying the mempool to make fee estimations easier, to more radical wording that any kind of filtering no matter what is censoring. I don't buy any of them as they all come out as words from an authoritarian leader who want everyone to fall in line.

Having more than one client makes the network stronger not weaker.

Just like the DNS system of the internet uses several different implementations of servers and clients and on nearly any kind of OS, so should Bitcoin.

The miners already filter based on their beliefs and jurisdiction. Changes made by core might make it impossible for them to keep doing what they do, for good or bad. But if 80% of the hash rate falls off the network, attacking the it becomes much easier for a state actor and they for sure would like to create chain reorgs now and then and they would have the power to do so.