Actually Makoa's pretty solid right now. He doesn't have kill power, but the thing is he and other off-tanks really shouldn't be able to consistently confirm kills. The fact he used to be able to do that, while having massive sustain made him broken for most of the game's lifespan. What he has now isn't nearly what it used to be, but you can confirm kills and still sustain rather well. Before this patch, I'd agree Makoa was pretty mediocre, but now Koa's actually good. Not only can you have decently consisent uptime on your ult, you can even reset your cooldowns by just pressing E. I mean of course without Leviathan, Makoa's not necessarily in a good spot.. But now the talent is so good with the proper usage that he's not only viable as an off-tank option, he's actually good.
And Khan and Torvald are abysmal examples. Both struggle to kill because their damage is very inconsistent. I rarely see a Khan get above 50k damage in a match and Torvald is even worse in terms of damage. I mean by the logic you employ in this post Corvus ought to be a viable damage champion, but yet he's not and in fact does not too much higher than average damage for healers, which of course is the lowest by role in most given competitive matches. The issue is that in practice you can't consistently deal all of this damage, especially at range while having to shield bot in the case of Torv, and in the case of Khan getting stuns and using shield/shout. But if this logic had any merit it would be even stronger now because Khan is the second worst tank in the game after the Vortex nerf and Resil buff.