Credits aren't the issue. There has to b a bottleneck to encourage spending and that is gear. Remember when there was no Credit Heist ? U really had to be selective.
I come from that time which is why I am sitting on 30 mil credits atm. Selective leveling. If i am not gonna put a character to at least gear X and omega their skills, they don't get leveled. No need.
Say u get a purple offense cross w/ crit, prot and speed secondaries. I lvl it to 3 to see if speed increases. If it does, I go to 6 and so on. If it won't touch double-digit speed minimum, it gets no more levels which saves credits.