I would point out that Lemon has played quite a bit of tank, and has enough knowledge on the role to be a well respected member of the Overwatch Shoutcaster professional scene.
I could also point out that (as detailed in her video on the subject), she solicited advice and opinions from several players who play the game at high SR (she did the work), and essentially wrote a thesis paper on her changes and her theory behind the changes.
If it helps, I’ll point to what Flats, ml7, and every other creator who has participated in the Experimental Cards to date has said: balancing a game is incredibly complex and takes into account far more variables than most folks initially give it credit for.
I’ll also own some of the blame, as the process for feedback, and follow up can be improved. I’ll be working with the production team to improve the process for future collaborated cards, including additional “milestone check-ins”.
TLDR: assigning blame to any one individual, especially for something as complex as a significant balance patch, oversimplifies something to a degree that I wouldn’t expect to see from someone with your posting history.