Well yes, in a division where you can weigh between 205-260 pounds strength can play a major roll simply because one guy can weigh 40-50 pounds more which is pretty much what we saw in that fight. But brock is not some slouch on the ground. Sure in a pure jj match mir is going to beat brock to no oblivion, but brock does have great wrestling technique which allowed him to get the takedowns and get in good control and keep it. If brock didnt have the wrestling advantage, his size wouldnt matter much which is exactly what cain showed us.
Which is pretty much exactly what your second point is stating. In a divisions other than HW, you will rarely see someone win directly because they are just that much stronger. The only exceptions to that are guys like diaz or bj who dont really weight train and could easily make lighter weight classes. But in the traditional cut 10-20 pounds you will rarely see such strength advantages but rather people dominating by their technique and talent.
In the same division outside of HW strength is never an issue at all. Your comment was technique > strength always, I was just pointing out that strength can overpower and outweigh technique in a fight, technique is not always superior to strength.
I agree that in a 10 pound weight difference it doesn't matter much, but that's because the amount of strength difference is minor, which is why I said if someone is a little stronger then it doesn't matter, but if they are A LOT stronger, it does, and someone who is much stronger can use that strength to power out of and control what happens on the ground.
Technique really does only get you so far, in sanctioned MMA divisions technique matters more then strength because of the division limit, but in the grand scheme of things strength is a giant contributor to a fight and can definitely be more important than technique, weight divisions are there for a reason.