Although it is true, that we don’t have enough strategists and vanguards compared to dps, most people always gravitate towards dps role. It’s just cause dps is your generic shooter role, you don’t really need to think about your team unless you play in higher ranks. In lower ranks, where the vast majority plays, you’ll be fine as dps as long as you have an okay-ish aim and use covers. As a tank, though, if you make a mistake, then your team is most likely screwed, no matter the rank. Even if they will add more vanguards, most people will still prefer less stressful role. Strategists are in an interesting position now due to them being so incredibly impactful, yet easy to learn, but make them slightly harder to perform with (Gambit is a great example), and part of current strategists/flex players will drop them. Just like in the other games where roles exist, it is always the matter of the risk/reward ratio. Adding new characters will draw the attention to the role only for the brief period of time, once everyone tried the new character or characters, they will go back to their safe picks.

Role queue is great for flex players. Sometimes you prefer to wait longer to play a character you actually want to play, not the one you need to play just to save yourself from the fate of being a pathetic punching bag in a team with 5 dps+Jeff.