I think everyone keeps missing something. There's more than fatigue costs. There's a charge time and Viola needs to concentrate to keep it active. It only lasts for 15 seconds, that's not a really long time. A stat buff can last between 1-2 and 5 minutes, usually.
I figured the drawbacks were sorta worse than the benefits. I could up the concentration requirements for Viola so she literally can't do anything at all while the person is hasted? Instead of just defend herself weakly and walk about. As in, stands still, full concentration on keeping the move up, can't divert her concentration to anything else. This isn't a "stat increase". This is a "I buff someone to let them do twice as much while I can't do anything of worth, and it tired them out a lot and I get fairly tired as well - possibly more if they're crazy with burst movement or SS".
I figured the drawbacks were sorta worse than the benefits. I could up the concentration requirements for Viola so she literally can't do anything at all while the person is hasted? Instead of just defend herself weakly and walk about. As in, stands still, full concentration on keeping the move up, can't divert her concentration to anything else. This isn't a "stat increase". This is a "I buff someone to let them do twice as much while I can't do anything of worth, and it tired them out a lot and I get fairly tired as well - possibly more if they're crazy with burst movement or SS".