This is complete nonsense. One of the fabulous things about writing is that there are no absolutes. Stuff gets published that I think is poor writing, stuff I think is brilliant languishes on the slush pile. I didn't find the Da Vinci Code to be a page-turner; millions agree with me, and millions disagree. I've used the opening of Enduring Love in class as a brilliant example of suspense only for some students to find it boring.
It's opinion! It's taste! Yes, there's informed opinion and informed taste, but that's no excuse for a teacher for insisting that their opinions and taste matter to the exclusion of anyone else's. And the same is true of any reader.
I've been in situations where someone I've asked for feedback has given it, and then gone the extra mile in insisting on their opinion - it's easily done when one is passionate about writing and feels one 'knows' what the problem/solution is. It's one of the jobs of a workshop leader to control and, if necessary, deflect a toxic reader but if the workshop leader is the toxic reader then you have a problem.
If you're ever in a class or feedback group where you're exposed to a toxic reader, take a deep breath and keep quiet. Don't argue - it will only entrench their opinion. If you say as little as possible there's nothing for them to push against. Keep telling yourself that it's your work and you can do whatever you want with it, that it's only one person's opinion. And then get out of the situation as soon as you can. Above all, don't take what one person says to heart, however published that person may be.