hey…I am the preacher for long and low bikes. I’m all about going UP form a low stack height (especially for a TT bike). When Specialized went to the Shiv Tri geo, they eliminated me as a customer. I literally could not fit on one of those bikes.
But you are kinda comparing apples & oranges here…a road bike and tri bike are different beasts entirely. Having a slightly higher stack on a new version of the Aeroad doesn’t mean that it is a “more comfortable” geometry. Again, the Aeroad had one of the lowest, if not the lowest, stack heights for road bikes. I haven’t looked at the actual geos for the new model yet, but a few extra mm are not gonna be a huge deal for the overwhelming majority of their customers.
Also worth noting that a frame structure tends to be more aero than spacers, although that delta has certainly been reduced with the advent of fully integrated cockpits.