IMO, they kinda already did us a favor by doing this in the first place. Originally we'd have to contact them directly, wait a few days/weeks, then get "one" refund and it ends there. What just happened here is they sped up the process of refund and raised our refund chances by 300%
So if anything, no one should be complaining at this point.
Also by your first suggestion of the 3 months 1 credit. It can be abused.
Buy 1 champ>Refund 2 months and 30/31 days later, get IP back and get the refund point 1 day after. Can be done for up to 2 champs if bought at slight time gaps(a month give or take) from the last purchase.