In 5v5 I’m ranked at Gold 2 and in 6v6 I’m Plat 2.
Maybe, I just play better in 6v6, it’s possible, but a whole division better?
I mean, don’t get me wrong, I’d like to believe so, but more likely is that 6v6 is just much less competitive atm than 5v5 is.
But I want to know what your experience has been, do you think 6v6 is less competitive? or does it feel about the same to you?
I think it’s something completely different.
Because before 5v5, in 6v6, I was ~Gold rank/MMR.
In OW2 and 5v5, I’m Bronze/Silver - but I didn’t feel like I was playing worse.
The thing is in 5v5, the weight of each player is more vital compared to 6v6.
In 6v6 it promotes more team play, however, in 5v5; team play still reign supreme, but individual performance is more weighted.
Thing dies more quickly in 6v6 compared to 5v5, but in 5v5; if you are down a player- it is normally a lost fight typically.
I was plat in RQ (currently unplaced, since I play M2T Comp instead), and I’m plat in M2T Comp. 
M2T’s bound to be less competitive, strictly speaking, because it’s a side mode with that much less traffic. But I suspect that your success in one and not the other is either about you as a player, or you’re on a good streak and are going to get a nasty shock very shortly. I was on the verge of hitting diamond with a 65% win rate, and then I ran into a whole bunch of games that brought that number down significantly. C’est la vie.
I don’t know about more competitive or not. In my experience I’m always ranked higher in open Q than normal. My theory is that less people play open Q (now 6v6) and that that’s the reason I’m ranked higher somehow.
In my case. It was the opposite. In 6v6 i was a bronze tank but in 5v5. I’m in Plat. For DPS/Support. I was Bronze/Silver in 6v6 and in 5v5 i’m in Gold.
Though i prefer 6v6 it’s way much fun than 5v5.