I really don'nt get why you won't give up, Salmon. People like you are the same people who make Mundo effective in the first place.
I've said all there really is to say about it. I just don't play Mundo anymore, because most teams I play against are that super-coordinated. It might have something to do with my wife having almost 2000 wins. She plays this game WAY too fucking much. I rarely lose a game when I'm not playing with her.
I just keep getting hit with ignites and equivalent with such amazingly precise timing almost every time I play him, and consecutive applications of these things often enough. At a certain level of play, consistency becomes incredibly important. You have to make precise intuitive judgment calls on when to engage and disengage based on how much combined punishment your character can take and dish out compared to the other team. If anything throws off your feel for exactly how much you can survive and what you can accomplish before you get killed or forced out, then things go to hell very quickly. Being forced to drop a large chunk of movement speed and health regen for a quicksilver sash causes me to overestimate my ability to engage and disengage. Healing debuffs throw a huge amount of variability into how much I am able to draw focus.
Yeah, it's still a ton of healing, even with the debuff, but imagine this kind of weakness on any other character. Imagine you're an AP nuke and think "I can drop that guy instantly if I jump in right.... NOW", but the enemy drops a summoner's spell on you that drops your AP by half. Now you don't explode that guy, and you're helpless in the aftermath of your miscalculation, as you're out of position with everything on cooldown.
And regardless of the numbers, everything I'm saying is based on hundreds of game's worth of experience. Mundo is by far my favorite character to play, and I don't enjoy drifting away from him. I just don't do as well with him anymore as I do with other characters, even though I know him better than any other character. I think the sole reason is because they're just more consistent. I'm not forced to doubt "Well, we could win this fight right now if I don't get an ignite dropped on me" and constantly gamble on how effective I will be.