When am I ever going to be in a game where you have spent 300k mass on GC?
I think at that point you could have just built a Yolona then 1 shot them all.
Anyway, you bring up several points in your post that are some what disjointed.
As to ahwassa:
Ahwassa is also a very good counter. If enemy is building 10 GC then you would outrageously win air. You could get by on 2 Ahwassa. Although for killing single targets its more efficient just to use normal bombers.
As to the TLDR
Now you've changed from 10GC to 3 GC and 12k in ASF. if that was the case then you could coutner 3 GC with 15k ASF and the other 56k in bombers. For reference you get 250 dmg a pass on t1 bomber which is roughly 2.7 dmg per mass. So for 56K mass you get about 150k frontload damage. Meaning you would kill 1.5GC per pass. So you can kill 3 GC in 2 passes, this would be 620 or so t1 bombers. Or you could use 100 Notha which is roughly 40k mass. Or 30 Sintha which is about 60k mass.
I mean at this point you could also just kill the GC with a t3 mix of sniper bots and shield bots. Or you could use OC Sacu. There's lots of choices for Seraphim.
Spamming all mass on only GC is very dumb, and you won't ever see that in a game, you will see mixed armies, such as GC with mobile shields, flacks, and some sniper bots, or Harbs.
As it currently stands a Yotha can already kill 2 GC with some support of T3 mobile shields. And Yotha is much better than a GC at killing t3 clumps. So this may inadvertantly cause Yotha based t3 armies to dominate at the earl T4 stage.