Judging purely by the situation, Qingyu seemed to have come off slightly worse.
After drawing all the aggression onto itself, Amoonguss had not only been hit by Encore, leaving it stuck repeating Rage Powder, but had also been paralyzed by Thunder Wave. Its speed had plummeted, and it might even struggle to use its moves.
But...
You had to give something up to gain something. Thanks to Shield Mushroom's support, its teammate Salamence had not only completed its Mega Evolution smoothly, but also seized the chance to use Dragon Dance. Those successive boosts had taken its fighting power to a whole new level.
Besides, those drawbacks were practically negligible for Shield Mushroom.
Its base Speed was only 30 to begin with, making it an excellent choice even for a Trick Room Team. Losing speed hardly mattered.
In Pokémon battles, speed was relative. Higher speed meant a better chance of moving first, so even a small reduction to 100 Speed could be devastating, whereas cutting 30 Speed by 20 might actually be a good thing.
As for Encore locking it into one move...
Shield Mushroom's role in this match had always been to tank and draw aggression so Salamence could run wild. Even without the move lock, Qingyu would probably have kept ordering it to use Rage Powder.
The only real concern was bad luck causing repeated full paralysis, but he still had room for error.
Even if Shield Mushroom couldn't move, those two opponents would have a very hard time focusing Salamence down. Besides, Salamence had Roost to reliably restore its health.
Ultimately, it came back to the same problem: Electric-types were far too weak at breaking through defenses, and lacked explosive firepower.
In the competitive battles of his previous life, almost all the relatively common Electric-type attackers had been