I tracked tank picks on both teams (all of them, not just start of game) for 2 long sessions and they don’t look very close to truly random.
Monkey : 66
Ram : 64
Ball : 59
Sigma : 55
Queen : 51
Orisa : 51
DVa : 47
Mauga : 45
Zarya : 43
Doom : 40
Hog : 39
Rein : 39
It’s very noticeable in-game that the top-2 are appearing way more often than others. I got Ram 4 times in 1 game for example. And I’ve had Sigma 3 times. I’ve never even had hog twice in a game.
I did this over 2 long sessions, yesterday and today, and the difference between top and bottom was similar in both sessions with some slight re-ordering at the top, so it’s not just some anomaly.
There seems to be even less RNG in DPS. I see mei almost every single game, and symmetra is way more common than most heroes. Torb is also up there. I see Genji almost never - it really stands out when he is selected because it’s so long since the last time I saw him. Cass is also very rare.
Unfortunately the RNG for DPS means I’ve faced 2 meis or 2 symmetras or 2 torbs several times. Sombra and Widow hardly ever appear (a good thing).
There is definitely something fishy about the RNG. It’s as if they have changed the weighting to make less popular heroes (to play against) have a lower selection weight. Not exactly what you would expect from MH though.