can't see your info but at a glance, it's just not a very strong team to take on a rex/phoenix. with no rex, yes. but you really don't have anything on your Empire team to stop the onslaught.
it's often strategy over galactic power. for example, a lower gear sith trio can often beat a full team of 5 geos. a single wampa (omnicron) can sometimes beat gas, grievous , and other teams. low gear gungans or iden can slaughter some relic teams. in every case, there's a huge gp difference. it's a matter of countering abilities. like Pokémon lol a water creature could probably beat a stronger fire monster (I'm not a poke expert)
it allows for variety. that way the same teams don't dominate every single mode like tb,tw,gac, etc.
I do understand your frustration. I'm a lil under 12 mil gp. I could not imagine starting over with limited team options and long grinds just for one team. unless you whale or become super efficient those are just the dues.
I sometimes lose to much lower Gp's because they outplay me on defense. but usually because rngeezus abandons me