not entirely sure why people are putting so much emphasis on rollers.
my initial impression from looking at the mechanics was that the game's focus is on movement and ink control. aim isn't that important, and every other factor (territory control, momentum, etc) stems from these two factors. rollers aren't great at either. it might seem like they're good for the latter because of how much ground they cover, but let's be real here, that's mainly because it's almost impossible to be bad at using a roller to spread ink. what you're observing is a roller being used the only way it can be while the projectile weapons are being used badly by people who have had a grand total of zero minutes in the lab figuring out how to spread ink properly with other weapons.
now before everyone loses their collective heads, consider that the roller has basically no way of spreading ink long range outside of specials (which their high ink consumption and less squid form use renders inefficient). meanwhile, every other weapon in the demo is able to quickly and easily set up ink trails just about anywhere. perhaps having a roller to deal with tight corridors would be nice, but having more than one kills your ability to move in a fight. with proper ink spreading and movement you can very quickly and easily strafe around people using just about any projectile weapon. it gives you tactical options, and from my experience with shooters, tactical options tend to imply better weapons.
this is all particularly important when you try to make a comp around a team with rollers in it. if you run 2 roller/1 sniper/1 ar, what do you do when your ranged players get bopped? respawn timers might not seem that long, but considering how fast a couple people could coat an entire area (all the while building special), if you're stuck with two immobile players and nowhere for them to go, you're just going to get specials and secondaries chained on you over and over again. one roller--again, how would you regain momentum when you start dropping?
naturally, this is coming from someone who also spent zero minutes in the lab, but I have no reason to suspect that rollers would be good beyond certain specific circumstances. perhaps I'm overplaying how well other weapons can do what rollers can, but I'm finding it hard to see how the lack of range and movement options could possibly be made up for.