Why? Because, quite frankly, the community doesn't really understand arena, for the most part.
I mean, look - I'm not going to say he's the best arena champ in the game. My only point is that, in the right situation, he can have value. For example, a team of UDK + Pythion + Ukko + Fortus, I think, could be quite strong on defense. It's hard to kill, has a buff strip + block buffs to enable Fortus, and scales forever.
Is it beatable? Of course it is. But, crucially, it satisfies one of the two primary objectives of a defense team - it *looks* beatable, but is deceptively strong.
And, as to what level of arena I play in? Well, right now, I basically don't play the game anymore, outside of just farming CB and Hydra. But, when I did care, I was G3 tag, and if I'd bothered to spend the effort, could easily be G4.
Fortus is bugged, Plarium tell 10% for each fear to scale but it isn't real. If in your team Fortus has Acc, which base defense can get, 2k? This champ need to be revisited.
E.G.: Fears placed cannot be resisted, or fix his moltiplier.
This champ is a shit and Plarium has lied theirs players, remember 80 Void shards. Plarim He said to fix it, but it didn't