Most personal trainers and none pro level strength and conditioning coaches don't know **** about actually getting significantly strong. Text books in college only go so far and I know that because I been down that road too. I'm not talking 300lb benches and 400lb squats, anybody can get that far with some effort, half assed diet and half assed training principles.
I've squatted 605 parralel for 2 reps at 6ft and my main priorities have never been strength. I don't ever max out and those numbers were recorded on my 4th working set. 80% of my squat training is done above parallel and a large portion of it being box squat above parallel. Many of the strongest guys in the world do significant box squatting and above parallel work. Even on chest such as board presses, 2 board presses, etc. Explosive short ranges of motion build strength and power. There is also another concept to go with that. Training fragile (slow maximum range of motion nearly 100% of time) builds fragile muscles, tendons and joints opposed to explosion building resistance to jerky unpredictable motions encountered in real life and sports. I'm not talking about being reckless either. But explosion, body english, etc is necessary and should be trained regular. There is certainly a place for slow and controlled reps as well and I do plenty of those after my big lifts, but you won't get far just relying on training that way.
Now I don't know what Michael Grabner's squat looks like, but it does make me cringe when people take shots at those training above parallel. I mean seriously, the strongest guys in the world do it for a reason. Most of the people that have degrees in kinesiology, exercise science, strength and conditioning are the last people I would want advising me on getting bigger/stronger. They are typically people who only studied and have zero clue of what it actually takes to reach elite strength levels. These people from my personal experience are the first ones to knock someone much more advanced in training when they themselves are a measly 170lbs looking like a casual gym goer.