The "Goku struggles to lift 40 tons" is from Toriyama.
https://cdn.discordapp.com/attachmen...49/unknown.png
(Dragon Ball#428)
It's not even the only time something like that was done too, Goku in saiyan saga struggled to walk in a planet with 10x Earth's gravity despite being strong enough to tank bullets since he was a kid, and he became far stronger since then, he's strong enough to push a boulder as a kid but then his adult self can't really lift 40 tons in base form.
There's also a funny case with Dr. Briefs, he talks like it's completely absurd for Vegeta to be able to train in 300x Earth's gravity, despite Vegeta showing up as strong enough to destroy planets and he's far stronger now although, at the very least the last one you can excuse as Briefs not knowing just how strong the characters are... Which's undermined by Vegeta looking tired in the single panel we see him training, so Briefs had a point, but regardless, it's talked like being able to walk around when your own body is 18 tons is absurd:
https://cdn.discordapp.com/attachmen...10/unknown.png
(DB#336)
So, basically, DB works on rule of cool, it's not exactly consistent, Toei makes the consistency worse, but Toriyama himself has his own consistency issues, at the very least, the power levels work accurately under Toriyama, something you can't say about Toei a lot of the times.