Personally, I think that the best fix would have "maximize spell damage, 0 spell damage percent" ignore spell damage percent, while "maximize spell damage" considers spell damage percent as a tiebreaker, doing what it does now.
Even better would be the option to use something like "maximize spell damage, (numeric_modifier('spell damage')+40)/100 spell damage percent". Right now, the closest I can get to that is "ash cli_execute("maximize spell damage"); cli_execute("maximize spell damage,"+(numeric_modifier("spell damage")+40)/100+" spell damage percent");", which is generally more than I would like to type. Also, it doesn't seem like it'd be quite perfect -- if you're changing equips, the max spell damage will change. The only way for this to be accurate would be to consider percent modifiers after absolute modifiers.