The misconception that you need 4 5* units to exceed 4000 points in Arena needs to be dispelled if it hasn't already.
Yup. Every time it gets brought up I'm just ... "no, that's not how it works at all guys come on." Off-hand, the total stat pool you need is 600, with the bonus unit, to get to 600 points per win? Since it's bonus * ([AvgStat] + 150) for the rating formula if I recall.
Get one or two 5*s to bring up the average and as long as your other units aren't like 130 BST guys (4* mounted mages are in the 140s still), you're probably approaching, if not breaking, the 600 point per match mark. That's a 4200-ish flawless run? You can't expect to go perfect but that's still two, maybe three, deaths to still get by 4000. It's a lot easier than people give it credit for to at least have access to the possibility of going that high. Then you just gotta win.