There have been 51 percent attacks on multiple coins, what are you talking about? Everything you wrote is irrelevant. The only thing and I mean the only thing stopping people from targeting Bitcoin is the cost in doing so. It makes more economic sense to attack smaller cryptos but, it is possible. Especially as computing power grows and decreases in cost. I don't need you to editorialize why YOU THINK it wouldn't happen, I was merely making the comment that its a possibility and it is.
It's shadowy dark money groups, billionaires, groups with wealthy backers...so when I say large mining groups have control, this is what I mean
The pow system prioritizes miners who can "crack the code" the fastest (speaking in the simplest of terms here). Wealthy groups have the resources to buy the most computing power. To ensure they continue to make money from mining, its in their interest to consolidate with other large mining groups. So yes, a few wealthy parties end up controlling the system