If pro players make tweets such as "x player is our support" then yes I think teams have roles and players have either more passive or more aggressive assignments on a team, I mean you're either AWPing, entrying, lurking, or setting up an execute/map control on T side (supports and IGLs), theres only so many things you can be doing and players usually prefer doing one of those things.
Support is also defined by how much freedom you have, despite that coldzera is a support he us allowed to rotate what part of the map he plays on T side because it is not his job to take map control, hes also allowed to secondary AWP which nets kills due to his skill and gets the CT spots where hes comfortable as opposed to Taco who is always holding a part of the map (squeaky, palace) and always taking early contact.
Usually the focus of the team is just the player with the highest overall skill level. Hence why I said there are star awpers, entries, lurks, and supports.
Teams do have structure and teams do focus on enabling certain players on their teams based on their strengths and that is a fact. No one would consider Taco a great aimer, but he knows the game very well, has good utility usage, and great comms, and theres a role for that.
Also if you consider coldzera the support then they have entry/2nd entry/lurk/igl(awp)/support
So no player is the star player? The centerpiece of the team? Every team has a centerpiece or duo that they focus on enabling.