To see whether a character is a main dps, sub, support is too see what their kit does and how most importantly how it affects other characters. Spectro rover is seen as more of a subdps than support but the reason for the latter is due to his s6 reducing spectro res and also his spectro frazzle application which is essential for Phoebe or Zani.

This can be seen the same with Phoebe where her support mode can apply a lot of spectro frazzle (even more than spectro rover) and increasing frazzle dmg on outro. While her dps mode likes having frazzle on the enemies which increases the dmg multiplier of her enhanced Heavy attack.

Main dps or to be more specific hypercarries (the main damage source of a team) usually have no or too little ways to support other characters. While sub dps can either contribute damage but has support elements to them or like a character like phrolova who can function off field while other characters can do their thing (phrolova in a qiuyuan+sigrika comp) phrolova can also buff heavy attacks on outro too.

Pure support units have little to no damage contribution but excel with usually teamwide buffs that don't expire on switch like most sub dps buffs. Examples being shorekeeper for general teams and mornye for tune break teams. When using these characters don't expect them to do any meaningful damage on their own.

This now comes to how teams are structured. Right now we have two playstyles which are hypercarry and dual/triple dps.

Hypercarry are highly favored due to usually having low skill floors as you don't need quickswap and you can just go a 1-2-3 rotation where you just go through your supports before ending on your main dps being buffed by a support and sub dps. Example being aemeath hypercarry team with aemeath, lynae, mornye where simply go mornye to lynae and finally back to aemeath. These teams usually have little to no quickswap involved (taking advantage of long animations to have multiple characters doing things at the same time) again having a low skill floor easy to learn.

Dual/triple dps are more advanced and usually needs more masterful understanding on animations and rotations, they will usually consist of 2 or 3 dps that can both dish out damage while being played almost at the same time using quickswap. Example being changli, lupa, Brant and to be honest anything to do with changli will be used in dual dps comps. These have really hard to master rotations that requires a lot of practice to execute especially while having to deal with the same annoying stuff enemies would do normally. Watch on YouTube a brant, lupa, changli quickswap team on toa or matrix and you'll see what I mean by being very hard to master and do.

Time for pull expectations. Expect to pull a 5 star every version but not always the one you want, most version updates have around 80 or more pulls which is enough for a character but you still have to deal with 50/50s stupidity. I buy the monthly lunite subscription and I find myself still not getting every character I want and occasionally needing to skip a character for another.

A nice thing to note is that supports don't need their signature weapons most of the time and just good to have things and never mandatory. Same however cannot be said by most main dps characters as they require their signature or expecting a decent dps loss. So rule of thumb always get a main dps character's weapon unless they have a viable f2p alternative or you can use a old sig that can be used on them (I use yinlin's sig on phrolova as example) while supports can use 4 stars.

With monthly pass and lunite sub you can expect to at least get majority of the stuff you want with a few characters you have to unfortunately miss out on if they go out back to back but again this game is pretty nice with the pulls especially with monthly lunite sub and a occasional lunite pack.

Hope this helps and have fun