Range is inherently a positive attribute, no? You can't change that. You can say, melees will generally get higher base stats and more mobility, etc etc, but it's not like Riot is unaware of range being range because they already do that kinda stuff.
But largely they're not doing a terrible job currently, seeing as the most common top lane / jungle picks tend to be melee. Now the current meta kinda favors melees with CC/mobility over damage alone, but that's a more complex issue. But as far as Mallet goes, we have a fairly underused item because most melees being played don't rely on mallet, and because Kennen is now typically played as an AP. Gnar still remains a decent pick in competitive, if I remember correctly, but not so much in soloQ, and he is the biggest Mallet user.
What about ADCs? Well, we're looking at even Kog, the most common Mallet user, only building it about 5% of the time. Kalista? 1%. Vayne even lower. It's what I would call statistically insignificant, as much as you may dislike playing against it - and I highly doubt you even play against it much.