Yeah, may be stretching a little, but works better in giving them more of a gap over the other Z warriors, who were trash, fitting Kami and Popo comfortably below them (actually, Kami was wayyy below them), and also has backing when we see the immense difference there was between weighted Goku and non-weighted Goku at the 23rd Budokai, with weight Goku being ~ Tenshinhan... And the jump in power being not well represented there. And since Veegta told Nappa straight away the readings didn't mean anything, not only due to amp chi blasts, as can be seen when they fought the Saibaimen, and Goku and Piccolo had already been through that level of chi mastery... Then I think it has at least a solid backing. Raditz at least stated their defenses were more solid than he expected when he attacked them and was surprised by Goku's tenacity of not falling down when Goku challenged him h2h, so there's some surprise from Raditz too when fighting them h2h. Maybe not the surprise from such a big jump? Eh, maybe.
I sometimes also like to assume Tenshinhan grasped some concepts when it comes to suppression, he was already more in tune with chi than the others and saw first handed the way Goku could read chi while not looking, so maybe he was alreeady in a stage a little ahead and could suppress a little, with the 250 reading of him being, perhaps, not his FP. Likely not Toriyama's intention, but eh, Ten was even with weighted Goku in the 23rd Budokai, so it doesn't hurt having him at 315 or so when FP. It also gives more of a gap between him and Kuririn, which 250 vs 206 just doesn't seem to cut given their different levels in the Budokai.
Like
23rd
Yamcha 165
Kuririn 185
Weighted Goku
-- speed 225
-- strength 280
Tenshinhan 275
Mr. Popo 340
No weight Goku (vs ten) 375
Kami/Shen 450
Goku/Piccolo FP 680
BoZ
Yamcha 177
Kuririn 206
Tenshinhan 315
Goku 334
Popo 340
Goku no weights 408
Kami sama 450
Goku/Piccolo FP 800
KMHMH 924
Makankosappo 1,330
Well... I think most ppl would think of it as hogwash lol