It's only beneficial if someone wins.
Thunder Armor was "DEM" because Swellow
was "DEM" because Skitty won Squirtle
was cheap because Squirtle won Pikachu
was cheap because Pikachu won
Ash using his Kanto Pokemon against Brandon was cheap because they won.
No one says something is cheap or DEM when the DEM Pokemon loses despite some impossible event that occurred. Why should this battle be counted as cheap or DEM? I mean it isn't like the writers have been consistent with its strength, I mean remember how many hits Pikachu took during the full battle (including Burn?).
If the writers want something to lose they'll make it lose really quickly if said Pokemon has no further benefit. It has nothing to do with strength or weakness or the portrayal, otherwise Ash's Pokemon got really screwed over the "years."
But see here's where the double standard thing applies in this case. The only people who are even going to "complain" that Pikachu is overpowered in this episode, is because Pikachu isn't their favorite Pokemon on Ash's Team. Oh no but if certain fans have some Pokemon on some ridiculous pedestals three things can occur: 1. Pokemon gets knocked out easily; those fans complain. 2. Pokemon takes a lot of hits and loses; Fans complain (except maybe in the case of an E4 member), and finally 3. Pokemon takes out two-three of opposing trainers' Pokemon and suddenly it's the strongest Pokemon Ash has ever had.
I mean the only reason to complain, is it's because its Pikachu. No other reason other than "Darn rotten rodent managed to last longer than other two." Besides even ignoring the biasness and ridiculousness, you have to think of all the incredible real life stories that occurred (and no don't agrue, these actually occurred). A woman's child is stuck under a vehicle and due to some (biochemical; I think that's the word) reason said woman is capable of lifting the vehicle up just enough to get her child out. How does this apply to Pikachu? Pikachu was Ash's last chance to do anything. Pikachu knows this, it could have forced itself to keep battling until the very last moment where it just could not. Sometimes things happen unexpectedly and you fall unconscious easily. Other times you can force yourself and you can last longer. Case in point: Sometimes when I overexert myself when it comes to lifting I end up almost or actually vomiting, and this isn't something that took minutes, this just basically for lifting up a couch for like 30 seconds (at most). Other times I can last hours when I'm playing a sport or having fun for example.
Human biology is very random, it's not always constant. This can be applied to Pikachu because the writers don't keep strength constant. I'm almost positive that Ash's Pokemon (or any other Pokemon) have their ups and downs just like real humans do.