Staying in G4 is far easier than you think, the yellow/red progress bar is completely bugged so you have no clue where the cutline will be. But generally 1000+ (always red) is safe. 1050 (again will show red) is 100% from my experience.
And I concur with your strategy, which is why I am gainst any changes other than bigger tiers. G2 - G4 really makes no difference in rewards/cvc points. Being G4 helps in a close Tag tourney for sure, or just to blow it up on day 1 and scare everyone off with 10k points.
Interesting that this thread popped up today because I had no idea where this conversation was located to come back to.
I decided to hold G4 Tag this week (first time I have not just farmed bars all week and fallen back to G3 intentionally), and with my weak-sauce defense teams, it takes just as much work (maybe even more) to hold G4 as it does to promote from G3 to G4....of course, not having the promotion bar to guide you means having no clue how many points you actually need. I stayed in G4 with 1056, but the promotion bar was never anything but Red for the last three days of the week.
You have some serious Void Legos for a F2P player. The only truly Arena Meta Void I have is Siphi. A little bit of jelly over here for your roster. The WuKong you use in your third team is a menace. I fought your defense twice and both times he was the reason that team beat me. Nice build. On your second team, you might want to consider Bulwark on your Nekhret. I don't actually use Bulwark on any of my toons, but it is a common selection on Nekhret and it prevents Siphi from sleeping him effectively.
