Faster projectiles is in a weird spot partially because of base differences in projectile speed. The only way I can get Sparky to contribute meaningfully to damage done is by giving them 2 or 3 levels of Faster Projectiles AND give Icy Fat Projectiles (slower speed), but at least it's not a build ruining choice so I frequently use it as a safe pick when the other two options would negatively impact my goal. Danta's projectile speed seemingly makes it so this trait is a requirement for him to hit things before they die, besides bosses.
Studious is another of those safe options. I THOUGHT it being maxed was a requirement for some traits, but upon double checking it doesn't seem to be?
Fragile and Heated I basically can't defend. Technically a safe option but unlike the previous two don't really add anything past level 1. Both Icy and Sparky apply those debuffs in a wide area constantly, even with just level 1 it has pretty much eternal uptime.
Wonder if we'll get a "refresh trait choice" research like how there's "refresh hero choice". Though personally I'd make the trait refresh a "gain 1 charge (up to research level) every [X] waves" rather than "[X] rerolls per game".