Yes I did see the adverb discussion. Sometimes I just get in a rush to get the words in and one of those -ly buggers slips in, so I included it as something for test readers to highlight.
I took your adverb comment to mean an editor who highlighted adverb series. I think they are frowned upon, but can really be fun to write. So if someone highlighted a series, I'd take that to mean they didn't think it was as funny as I did.
As to your initial question, I know that I can easily cross the line and have to force myself to abstain based on the writer's experience level. This is hard to do in an online class; far easier when I have the chance to edit my responses judiciously the next day or sometimes more days before forwarding them off.
See, here is the problem with deep, gut wrenching painful edits in full brutality---you can learn a hell of a lot faster with the knife. Yet, the knife can literally kill and hurt someone that you really know can be a terrific writer. The knife too soon, and for you personally from the sounds of it, can blunt the creative urge, and even cut it out. Too often college professors, who are frustrated writers, can famously fall into this category. The same type of prof can edit an author's voice into their own assumption of how it should be--to the true detriment of the author!
If however you can take it for what was graciously given---a huge amount of your test reader's time and talent, then you will value it, even if turns out to be a bunch of crap in your opinion right now.
I know of at least one published author who was asked, "Why did this edit finally do the trick to get an agent?"
The answer was a heartfelt humility. "When absolutely no agent would look at it for over a year, I went back to those people who read and edited my work and took the time to crit it and then re-read them. This time, I listened and I changed--not only how I edited the manuscript, but how I wrote so I didn't repeat the same mistakes." I would surmise that if that same author continues to follow what was learned through those knife cuts, they will have several more books published. If they don't, and they fall back on what they were doing earlier, they will ultimately fail.
One more thing for you to consider when you ask test readers to crit, give them an idea of what you want and your level before they agree to read your work. If you are a beginning writer, then tell them and don't be disappointed when they turn you down for now. See, I have these alien freaky times when I simply want to edit the crap out of stuff. They are gifts for heaven for my own work, but far more difficult for other writers to accept. Also, I have limited time, and if you really want me to crit/edit your work and take the time to do so, then don't send me more of the same level of work the next time. It shows me that you didn't learn from it, you didn't listen, or you didn't care about my opinion. My time is valuable and if you love what I edit and you keep sending me more of the same to do the same? Then it's time you paid me for my work.
EVEN In that case, if I loved your work, I would continue to do it--but I'd have to really love it to drag me away from my own writing and editing. :-)
This explanation is like the chemistry teacher who sat down on his kid's bed thrilled to discuss the full facts about the Elements, but after an hour of boring the kid, he says, "But what does that have to do with Elephants?" So if I've bored you.... try reading it again in a couple years. :-)
Hugs and enjoy your writing!