Empire Squad without EP for R2?

I'd go for Tarkin lead. Snow is fine, and he's needed for DSTB too.

You can first try at g8 but I do think g9 is wiser

Curious as one who doesn't have either ep or r2 at 7stars
My roster is same as yours,
G10 GMT, G9 DV, G9 TFP, G8 RG, G8 Storm
had no difficulty in unlocking r2 at 5 star, but curious how it will do for 7 star

I beaten the event with G9 Palp, G11 Vader, G8 Tarkin, G8 RG and G8 Snowtrooper. EP was the last one Standing. There is a certain kill order. You won't be able to beat it at lvl 79.

https://forums.galaxy-of-heroes.starwars.ea.com/discussion/150457/how-hard-would-r2-t7-be-with-my-lineup#latest

This is my thread about me doing it without EP

Tarkin lead Vader TFP RG Storm did it.
Tarkin TFP Vader survived the battle.
It's surely doable at lvl 79.
I specified all my thoughts, strategy, modding, and etc on that thread. Hope it helps.
Check my empire roster since I haven't changed any mods from them after the event yet. It is also linked in the thread above.