Miners can merge, I don’t really see anything wrong with it. Even if they merge it still doesn’t stop the competition, there will still be that competition, because there are still other mining companies. Smaller companies of miners can decide to come together so that they will be able to get better rewards, it’s not bad. And moreover these days you can’t mine alone, it’s not like it used to be in the past when you can easily just buy a miner and stay at home and be mining with your computer, nah this time around you have to join a pool before you will be able to get rewards.
Even due to miners' consortium they may work together and may decide things like corporate but all will be possible until they face another competitor. I mean it is highly possible another big players to be joining bitcoin mining to compete against the current players. So, their unite will not work for them forever.
Miners merging causes centralization. When miners merge and form corporations, we are back in a centralized banking system and there is no new innovation going on there. Mind as well use Paypal or your web bank. They are probably also much faster than Bitcoin. A dynamic blocksize prevents miners from merging because they have no benefit from doing that.
