Knowing what squads to use against what squads is an increasingly important part of SWGOH. With the Grand Arena now in place, you can’t hide from Traya-lead teams and the like. Fortunately, you don’t need to have Traya or all the zetas on the nightmare team to beat it. There are counters to it that require easily farmed characters and just 1 zeta (aka Finn’s resistance team properly modded). To find how to beat a particularly hard team I advise checking on youtube by searching for “counter” and “swgoh” and the name of the difficult character or squad.
The featured image here is a helpful guide of what counters what, if a little dated. If it’s too small to read, Right-click it and “open image in a new window” or download it. There is more to it, but I’ll have to get my hands on it in its original form.