I did the math, and while T1 + T2 beats T5 turrets in DPS, albiet costs 4 times as much power and resources, and then, only by a small amount. (half of T1 damage)
Aside from Spider, ofc, which was broken to start with.
Spider, nerf to, at most, double stats of standard. It isn't even a normal tower type... You cant just multiply stats by 5 and expect it to not be OP as riot starship T4.
Anyhow. Change Core turret limit to 24 or 48 per planet, remove interferance (or don't), and all tiers still matter.
Or, the whole "Quarter cap limit per planet" plus three global limit placeable control nodes, each boosting cap by 1/4th cap on said planet. Core having same rules, and same three deployable nodes.
Would give you reasonable defences everywhere, and heavier at key planets. Keep Core controls at half normal cap, and still a quarter default everywhere. So 24 normal cap, 6 limit for all planets without node support.
Or, considering towers with cap of 12, may need to change it to a third cap default, and 2 control nodes. Considering 12/8 is a tower and a half....