I think the criticism is more about the process than anything else. We knew that Beecher was viewed as a high floor/low ceiling player at the draft and fans would have preferred using it on someone with more offensive potential. It doesn't help that two of the most popular names for that pick, Kaliyev and Brink, have both progressed well.
Now, I know there are people here who talk about how just getting an NHL player, even bottom 6 forward or bottom pairing defenseman, is a success because of the low chance of success with low 1sts. The problem is that since Sweeney took over, they've had two consistent issues, holes in the top 6 at wing and two aging top 6 Cs, neither of which have been properly addressed. People wanted them to take a chance on a player who could fill those roles, like they did with drafting Lysell last year.
I don't think anyone can ever expect a GM to never fail, but I think you use processes that give you the best chance at success and I don't believe Sweeney has done that. There's that famous line attributed to Einstein: "Insanity is doing the same thing over and over again and expecting different results". I feel like that line has described Sweeney for most of his tenure.