That is no longer a reasonable assumption.
Now that the understanding of the hydraulic mechanisms of expansion have fed into bullet design, expansion of hollowpoints is a significant factor in lethality.
Expansion must never be the basis for bullet selection, but considered a bonus when, and if, it occurs. Bullet selection should be determined based on penetration first, and the unexpanded diameter of the bullet second, as that is all the shooter can reliably expect.
I dunno, I've shot stacks of wet phone books with .44 mag semi wadcutter and semi wadcutter hollowpoint--Hornady XTP.
One beer case stuffed with wet phone books shot lengthwise hardly even slowed down the SWC's. However, the XTP hollow points generally stopped in the phone books, and showed expansion... Same weight 240gr and same load 23gr W-W 296.
Then again it may not be a good model for human tissue... I dunno...
Handgun bullets expand in the human target only 60-70% of the time at best. I think that when one considers stopping power of a handgun round it is best to assume worst case scenario (your hollow point does not expand 40% of the time). I do not think that all Julian Hatcher's information is out of date. The point of this article is that bullet weights over 179 grain that are .40 caliber or larger will penetrate more tissue and cause damage thereby hopefully defeating your opponent more effectively than smaller caliber speedy rounds. Some of the information may be incorrect but there are things we can learn from Hatcher's work.