Why do people say this was the strongest godzilla?

Two things, Godzilla didn't defeat Destroyer. The Japanese military did with their ridiculous cold weapons. And two, having a plane of all things being able to withstand a red spiral ray is patently absurd. I usually judge Godzilla's power based on what he can do, rather than what color his atomic ray is. The atomic ray did minimal damage to buildings even. It had little effect on Destroyer, and couldn't destroy a plane. A PLANE. Planes are never durable like that. If they were, we wouldn't have a use for any other military vehicle, as the planes would be invincible.

The weakness of his ray would be enough, but he also fought like a slug. He was way way too slow, and seemed to plod along at a snails pace.

As far as I'm concerned, this is the weakest godzilla I've seen so far.

Did anyone else seem to notice that Godzilla was also DYING in this film?

Im sure if you were gonna explode and/or meltdown youd feel pretty weak toooo.
Its seems like this was the whole point of the movie.. or atleast Junior being in it. The Elder one is dying and Junior takes his place.

And yes.. the plane WAS meant to withstand Godzillas attacks and any other radiation based obstacles it should encounter.

Godzilla was dying.
And Junior was well.. a *beep* teenager basicly.
That would be why they were both kinda weak.