Well, first off. Not all of them are weak. From 2006 on the 5 speed is just as reliable as most other transmissions.
Secondly, all the talk of chemistry.
A little history.
In the early 2000's Honda was in the process of morphing from a 'little econobox' company to something slightly more upscale. In this process they decided to design their own transmission, coming up with something akin to an automated manual box with clutch packs doing the work of shift forks. The downside to that is that during some shifts the transmission is simultaneously coming on and going off clutches on the same shaft. Get the timing wrong, or have too 'grabby' of a fluid in there and you end up with a jerky shift. Jerky shifts do not go well for customers wanting a more 'luxury' car.
So, in the early 2000's Z1 was formulated with an additive package allowing the clutches some slippage and smoothing out the shifts.
This is supported by language in the 2000 and 2003 owners manual that you can use Dex III, but be prepared for harsh shifting. Not damage, just uncomfortable shifts. (Prior to the 2000's Z1 wasn't a thing, although it was back-specced for some of the older transmissions)
DW1 came about with roughly the same additive package with supposed improved base oils as Z1 was apparently degrading rather quickly.
None of the aftermarket 'replacement' fluids come near the chemistry of DW1. So if you're looking for that, stick with DW1. If you're inside of warranty and doing your own maintenance, might want to stick with DW1, or keep excellent records.
My thinking is that you don't need the exact additive package to do the same function as DW1. You would think that Idemitsu, who probably knows exactly how the sauce is made would use it if they needed to in order to offer a 'suitable for' DW1 mix. The number of people using alternative fluids and not appearing to have problems, myself included, point to that particular additive package not being strictly necessary. My #2 Accord transmission has made it further on Idemitsu than the #1 one did. Is that proof? Not with a sample size of 1 it isn't, but it is the data I have.
There's nothing terribly special in a Honda transmission other than no brakes or bands (All clutch packs). They don't use special bearings, bushings, or metals, so any standard anti-wear chemistry should work just fine. They can probably be sensitive to viscosity due to the shift timing issue. According to Raybestos, they do have to use a special friction material in their Honda kits, likely to deal with the slippage necessary during shifting.
More debate here:
Three ATF's were analyzed by two labs, one a university lab and another a commercial lab to determine their elemental and chemical composition because of on-going debates about the suitability of each fluid for various applications. The three ATF's analyzed were: Genuine Honda DW-1, Valvoline...
bobistheoilguy.com
Some of the opinions above are my own, but I've been following the Z1/DW1 discussion from way back, and I feel as though there are some logical conclusions that can be drawn from all of the debate.