Sounds like you are uninformed or have just not been around for long enough, based on the way you phrased a lot of that.
She used to have a 2 second charm at all ranks for a long time. During a previous nerf it was made so that she only had half the charm time at rank 1, scaling up. It's not 'doubling for leveling the skill', it's the skill losing half of its cc early and getting it back later - literally the opposite of what you are saying.
During previous iterations of ahri, riot experimented with pushing her towards different kinds of play styles. They tried the standard mage thing, then they tried the assassin thing (they even made her charm cause the target to take % increased damage for a while), finally they said 'we think ahri is healthiest as a kiting mage' and took damage away from her in exchange for give her the Q movespeed to help her kite people around and get multiple spell rotations off without being ult reliant to kite.
Neither of those parts of ahri kit are thrown in there randomly, they were deliberately made that way during very visible updates where rioters were very vocal and open to the community about their balancing decisions.
Foxfire is already unreliable, each foxfire has its own small lock on radius around the fire as it rotates around ahri and if an enemy champion isn't basically in melee range from ahri when she activates her w in lane, the spell is almost a complete waste of mana as it will already fire at minions. During teamfights there are rarely any minions around anyway.
I suggest you do a bit more research about a champion before throwing out suggestions. As a protip - hacking away at mechanical aspects of a kit are the very absolute last things you want to consider touching on a champion to balance them if it is at all possible to bring them in line with base damage, ratios, or other minor changes. If your 'proposed buff/nerf' is going to have an impact on how someone is supposed to play the champion at all then you are looking in the wrong direction if the champion is healthy but just has a high winrate.