https://jaiminisbox.com/reader/read/boruto-naruto-next-generations/en/0/21/page/39That and the next page are the moment I assume you are talking about.
The Wood Dragon jutsu has the preexisting feature of negating other chakra absorption techniques. This, in my opinion, is the only reason it was able to stop the preta path.
My opinion is different in this regard:
http://naruto.wikia.com/wiki/Wood_Release:_Wood_Dragon_Technique (the trivia section)
http://ww2.readnaruto.com/chapter/naruto-chapter-656/If you scroll down to Hashirama's English dialogue, read from right to left order, he says:
That wood dragon will absorb chakra from you! Now your chakra-absorbing ninnjutsu are nullified and meaningless!
The wood dragon nullifies Madara's chakra absorption techniques because it absorbs chakra, not because it is some innate ability of the dragon's, at least according to Hashirama. This sticking point the wikia only added as trivia for the wood dragon and is not mentioned in the preta path article, despite that being one of the few times in the manga in which the preta path would have been bested.
Of course, it is entirely likely that this was used on Madara before he could activate Preta Path, but this is still a precedent of a chakra absorption jutsu being used to overpower and nullify the effects of the other.
Finally, my opinion regarding your Thesis:
That when two absorption techniques of similar power clash, they result in complete nullification of one another.
1) The Boruto manga had two of the exact same techniques with the same power against each other. Two chakra absorption techniques of equal power, just like two regular ninjutsus of the same strength as each other, cancel each other out. Therefore, unless "similar" is changed to "equal", as I see it, the thesis has no more supporting evidence now than it did when the dragon rolled up on Madara.
2) How are chakra absorption techniques ranked in terms of strength? Is it the power-ups behind them like most things? If that's the case might as well lump them in with every other jutsu scale.
3) Accepting this thesis would mean that barrier-wide and large area of effect chakra absorption techniques (Kirisame comes to mind here) theoretically can then be bypassed by using something akin to preta path or another chakra absorption barrier. It would reduce the utility of large scale chakra absorption barriers.