The role of Tanks and Fighters in the game

There's always been a lot of discussion about the place of Tanks in the game, because some argue that there's no clear difference between a Tank and a Fighter, therefore there's no reason to have both in the game.

Currently this is true, because a Tank is just a Fighter with less dmg and a bit more CC, basically a different kind of Fighter... With the current design Tanks can never be healthy or balanced since whenever a tank is viable, considering that he doesn't scale with any offensive statistics he just builds defense and this makes everyone feel sad, he feels bad because he is just a pile of defensive statistics unable to do anything (the fighters have almost as much CC as him but they deal a lot more dmg) as well as the opponents because they feel like there's nothing they can do to break someone so tanky.

I have an idea to separate Tanks from fighters and make em shine on their own, so a team can chose to pick a Tank over a Fighter if the situation demands it, but more importantly, to bring diversity to campions by increasing the strong points a class. The idea is to do the same with Tanks that was done to Supports last season: make it so that a Tank's utility scales with an offensive statistic. This approach will mean that a Tank will need to balance his offensive and defensive buys (just like a Fighter) and the more offensive they go, the riskyer it gets, but the higher the reward will be as well. This means that a Tank will have a real say in how much tanky he needs to get according to the situation without just giving em damage and making em the same as Fighters. Let's make an example just to clarify (this example was created just to explain my thought process, this is by no means a suggestion as to how the champ should be reworked), Shen could have his e taunt duration increased based on his AP, his ult could teleport him to his ally faster scaling with AP, the heal from his q to his allies could also scale with AP, he could even have a slow on his passive that increases with AP as well.

What do you guys think?