Considering the sheer mass involved and the fact the animation still shows some significant moon present there they were certainly not out of line using a solid example to gauge power.
As for power stacking I am aware that Ichigo does not seem to be stacking his various forms throughout the series as were they, allowing him to stack them all at once in a multiplicative way was a way to give him more credit from a spiritual power perspective since Master Troll Kubo never gave consistent numbers for power levels and did very little to establish Ichigo's growth as the baseline power for various enemies constantly seemed to vary. Also the hole's depth is irrelevant since as you said we don't have a good shot of its depth, the best way to then calculate is to assume it is at least as deep as it is wide. If you feel there was a better method to calculate the power level other then allowing him to stack his forms by all means share.
And I get what you're saying, I rather despise the show at this point for its general lack of intelectial dishonesty, see my aformentioned complaint about a certain sand ninja getting burgled during his death match or the fact that they have twice had actual material from creators or in universe sources claiming who would win in a fight but went the other way. But there just isn't a lot of room to complain on this one. The best bet you would really have is to point out that Boruto's dad mentions that he has gotten rusty during some of the Boruto material and claim they used a version of him stronger then his current form.