In my opinion the shorter interval of the AHU/1Z timing belt has to do with the engine’s roller design, not the belt itself. I’m all for operating TDIs economically, but this is a “stepping over dollars to pick up dimes” scenario.
The ALH has more rollers, yes, although one of them is really only there to ensure there's adequate teeth on the water pump due to the angle at which the belt gets to the water pump after the injection pump.
The upper roller is the same principle, just not the identical part, to what the ALH has. So, with that in mind, realistically the only additional roller the ALH has is the one between the crank and the tensioner. That's already the slack side of the belt, but the 1Z/AHU uses a nearly identical tensioner to the ALH. Both are spring loaded/auto compensating.
There is an obvious construction sturdiness difference between the standard 1Z/AHU belts and the "100k mile" ALH belts... and bear in mind the early ALHs that have the similar, thinner, smooth backed belts were also rated at similar 60k mile intervals. It wasn't until they got thicker belts with that textured backing did they up the interval to 80k, then when they updated the lower roller between the water pump and crank to be a double row ball bearing instead of single row, they upped it to 100k.
Being that the 1Z/AHU does not drive the water pump, but does drive an intermediate shaft to at least be an intermediary between pump and crank, it literally only leaves the belt and the absence of the small lower roller between the crank and tensioner as the most notable changes. And I'm not sure I see how the absence of that single small roller on the slack side of the belt would actually create a significant difference in rated belt life. The early ALHs were rated at 60k too... And once again, there were obvious similarities in belt construction between 60k ALH belt and standard 1Z/AHU belt.
So, to me, when you find a belt like that Dayco that obviously is of the same construction as the much higher mileage ALH belt, I think it would be very safe to assume you could get longer life out of it than the standard belt being that the primary thing that allowed the ALH to uprate belt intervals was the belt itself (at least to 80k), and then the large lower roller upgrade allowed it to go all the way to 100k, which is of no consequence to the 1Z/AHU setup since it doesn't have any of that water pump or extra roller nonsense anyway.
But yes, the 1Z/AHU belt is an easier one to change. No engine mount or mount bracket to deal with, less parts to swap out when doing the belt as well, so all in all, it's not a difficult service to just keep doing at 60k regardless of belt used. Though for guys who've boosted performance of their early TDIs, I'd definitely feel a lot more secure having that much more durable and aggressive tooth design of the Dayco belt.