The larger issue is simply that GP doesn't actually represent "battle value" of your roster in any truly meaningful way.
As an incredibly oversimplified example, a 5*, 2z DMalak at g11 has the same GP as that vaunted tank at g12 with 1z - First Order Stormtrooper. 3z, 7* DR has less GP than CLS or JTR with 3z (and just a little more (about 2k difference) GP as zzKRU. So a zzKRU+ zFOS = zzzDR+zzMalak - at least in terms of GP. Therein lies one of the several issues that plague GP as a dominant factor in determining equal matchups.
The other is that a 6 dot mod counts as a 6 dot mod in GP - whether it has a speed secondary of +5 or +25. In a game that has historically been about speed, the fact that higher speeded mods are not somehow "weighted" in GP is extremely short-sighted.
A third issue is that g12+ gear is a tremendous boon stat-wise...but not really GP wise. And while the devs explained when g12 was released that it is a big jump - those numbers aren't accurately reflected in GP- at least not in terms of battle capability.
TL;DR - GP is a heavily flawed determining factor in actual "battle ability" of a roster, as it doesn't account for power creep of newer character kits/synergies, actual mod abilities (if it accounts for mods enough at all) or the power jump of g12+ gear.