In a situation where somebody instalocks DPS and then somebody chooses a third DPS last (imagine this hypothetical team has 2 healers, 1 tank, 3 dps), the person who instalocked is much more entitled to play DPS in my opinion. The person who chose last consciously went against what the team needed whereas the first person simply chose a free role.
Now if it was a couple of minutes into the game and the team was clearly losing with that team comp, it would be the fault of any of those 3 DPS, not just the one who picked DPS last. Any of the 3 could potentially flex onto the tank role now that it’s needed, once the team is in need the ‘I picked first’ argument is petty and if they really want to win they’d swap.