That's a bit of a shit argument, and I'm a Zerg who's has always believed in T being by far and away the hardest race.
Terran has the most involved mouse movement. This is the singular aspect that causes Terran players to suffer greater injuries, as splitting is one of the only physical elements of StarCraft 2. To argue difficulty from this point is really, really dumb. Your race could be incredibly easy, and have masses in the way of physical exertion. The opposite could also be true. You also have to look at play style, hard to execute or other wise.
Terran has always been the most active in their multitasking. Not quite as much going on in terms of base switching (a la Z), but you have drops, forced aggression, and bio. Nobody can deny that. They also cannot deny that it's one of the driving force's behind Terran injuries. Injuries however, aren't indicative of a harder race, just one detail of the race's focus/difficulty/ethos. If we were to declare a game difficult/high in skill cap based purely on mechanics, or even more arbitrarily on injuries, we should all stop playing SC. If any of its pro's ever put in the same kind of hours that the top SC players have, Quake 3 CPM and Smash Bros. Melee would both win that contest.
You argument might be that Terran has the highest mechanical skill cap, that most would agree with. Or that Terran has the most challenges when looking at mouse accuracy and hand speed, you'd be right. But to just say that it's the harder race based on a singular aspect of this hugely multi-faceted game is not smart. Remember in WoL, when Toss was incredibly weak? That wasn't due to mechanics, Protoss has always been the easiest in terms of hand speed etc. but in regards to strategy they needed to be much cleaner and this took time. Terran, like Zerg, is less strategical/creativity dependent. Meaning the best Protoss players had to rely on this entirely different skill set present in StarCraft.
It doesn't help that the majority of Koreans seem to have atrocious posture (especially Maru) and use the Logitech G9x, which contorts the hand in a very unnatural way for most people.
The power of a race, and its difficulty to use comes from the difficulty to win, and nothing else. If T is winning the most, through mechanical prowess or otherwise, it's the easiest to win with, and as such the easiest (unless there's some kind of massive anomaly in regards to a race's player base. Hypothetically, all the innately StarCraft gifted people in the world could play one race by chance and inflate its power. This isn't the case, but it could be.) This hasn't been true for T since WoL, but that's how that word works.
I thought you were a mech player. Pretty sure I've seen you post a mech tutorial video anyway. Not too sure you're allowed the T superiority complex if you play mech.