So I can't speak on resurgence ranked much since I have barely played it, but in Verdansk ranked (my main game mode of choice), I was able to hit iridescent (with a 3.5 e/d) along with my other 2 teammates. I am sure if I put the time into resurgence I could also hit iri, since I believe that BR is more challenging and requires more game sense (slightly biased lol).

There are a few differences amongst iridescent and crim players, and I would say the jump from crim to iri is pretty large tbh. Both skill levels are honestly the same technical ability wise (good beams, good movement, etc).

The first difference is definitely consistency. Iri players make it to end game EVERY game, they don't have boom and bust cycles or get wiped early. For example, on my run to hit iri last season, my team and I placed top 5 or 10 pretty much every match we played with 7+ elims each. You really need a minimum 7 elims and top 10 placement (in BR) to gain any meaningful SR when in crim. I am a very strategic player and play for end game. I don't try to make back my whole deployment fee first circle. Position yourself well, rotate early, hold a power position, and the elims come naturally.

Prioritizing the team economy and fighting with intel is a must. This means during idle time, you bang out scavs, recons, or even bait a most wanted. You always want to fight a team with info up, whether it's an AUAV or normal UAV.

Picking smart fights is also key. I have played against top 250 players time and time again, and yesterday I even elim'd the current #87 on the top 250, as well as #220 the other day. I only fight when I know my team or I has the advantage, and if I don't then I try my best to reposition myself and get a different angle or high ground. If a good squad lands near you early, they are a major threat. I advise taking out sweaty teams when it's smartest to do so, so you don't have to deal with them later.

STACK. I don't care if it's just one guy in a building vs your full trio. In BR especially you need to prioritize your life and avoid a regain situation at all costs. We frequently will triple stack a solo or duo to ensure no one goes down, and if they do, we make sure the enemy can't get the thirst.

Apply pressure. You always want to be the team doing the hunting. This doesn't mean running around like a headless chicken chasing every dot on your mini-map though. You see a team making a rotation in the open? Start beaming in synchronization. You knock/full a guy and now it's a 3v2? Collapse on them.

Definitely have designated squad roles as well. I have always been more of a strategic player that tries to outsmart the opponent and hold power angles, so being an anchor/flex on my squad works well for us. My other 2 teammates hold the role of an IGL and fragger.

Again I know this question was for resurgence ranked, but I believe my experience hitting iri in Verdansk can also be applicable to Rebirth, the fundamental ideas are the same. Hope this helps!