I was not the DM for either of the my above examples, and the DM was not at fault for the PC being hectic with impatience.
In the first example I was one of the two players who had "purchased" a magic weapon instead of magic armor.
In the second example I was playing a PC who also was trapped on the wrong side of the wall of fire/gelatenous cube (but in a different hallway than the impatient player). I waited patiently and cautiously for the way to clear, rather than waste real time doing unnecessary actions -- I let those who were actually in combat on the other side use the time.
And neither situation was the DM's fault. In the first example, it was a random wilderness encounter in a "dead lands" environment (we knew there'd be undead about). In the second example, the wall of fire was put up by another PC (who didn't think through her placement of the wall).
As for "a DM that lets a PC be useless", what do you suggest? Ban hold person and sleep spells? Ban tactics by clever enemies to seperate or neutralize some PCs? Even if the DM designs every encounter to allow every PC some impact, a PC could do something to make a fellow PC "useless" (as in the second example). Or perhaps the DM should just make up more enemies so the temporarily useless PC has something to do?
DM: "OK, 10 orcs come running up from behind."
Player: "I thought we cleared out those rooms behind us."
DM: "Yeah, but Tom is bored because he can't hurt the golem, so I'm adding in some more enemies that he can fight."
Instead of blaming a DM, why can't players be patient for 5 minutes? Or perhaps find a way to be useful, like set up flanking, or draw attacks, etc.
So don't get all up on a high horse. The fall will hurt when someone pushes you off it.
Quasqueton