So currently rare/yellow means more than 2 affixes. Not ranks of affixes but individual affixes.
The thing is when I see a yellow drop my first thought is “99.99% chance of being junk”. When I see a blue with an prefix or suffix I care about I immediately pick it up. This is because the rare is going to have junk affixes I don’t care about. However that blue “Damage prefix of my build Swordname” is something I know I can make into something I want.
This disconnect between supposed rarity and actual value is most stark when doing monoliths and seeing the rewards for rare items. Why would I ever go for that? I’ll just get a pile of useless junk. How about instead of rare being “has 3 or 4 affixes” make rare “has a tier 4 or 5 affix”. Exalted already work on a similar system. So my suggestion is to apply this better value system to lower tier gear as well.