Here are the reasons:
- Avoidance is, in my opinion, the more useful potion effect, as you still aren't getting aggroed, but you can still find Pokemon you want like rare spawns or Shinies. I used it all the time prior to 9.1.4.
- There is no natural source of long-duration Avoidance. This incredibly useful effect is now practically unobtainable (getting it for only 10 seconds after a battle doesn't count, okay? You can't actually use that to hunt for Pokemon.). That is part of why the change of the Repel effect is my least favorite change in 9.1.4; it wouldn't bother me if I could get multiple minutes of Avoidance naturally.
- When you use the Scare moveskill, the message displayed in chat is "<Pokemon> intimidated the nearby Pokemon! They are too afraid to challenge you." Quote unquote "too afraid to challenge you". Sounds a lot more like Avoidance than Repel, am I right?
- This makes it so the Scare moveskill and Repels do different yet unique things, giving them both a niche.
I propose 10 minutes of Avoidance with a 5 minute cooldown.