Having one weak fast mana hitter (scarlet is a weak hitter, she’s only strong in combination with another multi-target hitter that lowers defense like Gormek or falcon) isn’t going to make raids that much different, but having a 70 defense debuffer will go a long way towards better titan damage.
IMO, things people should focus on when they are choosing their first and second set of 70s are: 1. titan damage, 2. completion of all rare quest stages, 3. event completion of epic and legendary (formerly intermediate and advanced).
Those things get you either guaranteed ascension items (event and quest) OR help move your alliance towards higher loot titans (and loot tiers). Things like raiding and AW should be secondary - it won’t kill you if it takes a bit longer to get raid chests filled and scarlett over gormek isn’t making your raid team any different.
EDIT - many of the top players are still using Gormek vs 10 star and up titans.