Criticism, in this context, comes as part and parcel of debate. I would though offer up ' voicing of opinion' as a more non confrontation tack. That's all well and good on forums.
I myself was in the camp of not seeing GB as a man who was IMO not going to deliver promotion to Prem. That was just me voicing opinion not criticism. I explained that my reasoning was that he seemed to me to be of a too cautious nature. This, I was taken to task on, which is fine because this is a forum. Who's to say if I was incorrectly concerned, we'll now never know.
Unfortunately subsequent selected managers were proven to be poorer.
Now with TM I have earlier voiced my similar minor concern, but this is at level div 1, not reaching for Prem. Plus, after the earlier two managers at least TM is a more palatable guy for both owners and supporters. Added to which we are actually in a reasonable position, despite your fears of us falling away.
Despite too many draws (which everyone agrees on) some of us feel that TM just may see the course out and deliver, whereas some see no hope. That's what causes the discord.
You say he has to learn fast, but I'm not too sure what this elder statesman manager at this level needs to learn?
If by this you mean be more bold / adventurous that's fine, and the adage 'fortune favours the brave' comes to mind.
However that is not always the case, far from it. Being too 'adventurous' is pushing your luck!
Even in my advanced years my outdoor exploits involve mountains an goin up em, no matter what.
Back in late sept I was scaling a new for me un conquered peak, an although it had snowed a couple of days before and this was a northern flank I battled regardless. I managed the peak because my obstinacy took over, but at the cost of minor frostbite on three fingers on both hands (in sufficiently prepared as it turned out).
I may have felt chuffed that I had endured the challenge, but on sober reflection gave myself a bit of a *******ing for being not a little stupid. That was criticism towards myself for sure.