Even if people upgraded to XT, hearn wouldn't have more control than any other devs.
The code is opensource. Normally, Devs can only propose ways, and the community can decide what turn to take.
Currently most posts and comments that go against Blockstream/Core devs are being censored on forums owned by theymos.
I think the sole reason behind the creation of Blockstream was to control bitcoin development.
Wrong, he would. You have made contradictory statements.
As you are implying, currently core devs have clearly more control over Bitcoin code than Gavin and Mike. If the latter two succeed with their fork, then XT becomes the real Bitcoin. As many of core devs leave (they have stated they likely will), the Bitcoin code gets under control of Gavin and Mike.
Of course, if they start malicious activity in the open, someone will notice, and some action will likely be taken. But it's not the only way to undermine Bitcoin -- you can engineer trivially looking patches that introduce actual weaknesses which almost noone can notice until it's too late.
I'm not implying they will necessarily act maliciously, I'm pointing out the fact that if they do, it can go unnoticed. There are very few people with enough expertise to notice that, and most of them work for your odious Blockstream...