For me personally - Athena is great hero for flanking green tank, cause she’s strong against red. Greg is slower than Lianna and his crit buff is not that much impactful in defense imo. The def drop Athena has is the best defense down in the game, it’s really good on titans, I went as much attack as possible on emblems with her too.
I personally got Alasie and Athena at +19 and next bunch of ranger emblems will go to Gregorion. I reseted Gregorion for Athena when I got her about 1.5 months ago and I don’t regret it. I use all 3 heroes a lot in offense, but Alasie/Athena also in defense. I’m just used to the green tank being most popular and Greg is not a tank, but I also don’t think he’s that impactful for different tank color defense setups. I rarely meet him in defense when raiding in diamond rank.