Quite the opposite IMO:
* Blueprints have been proven by the test of time to be very stable.
* As
@Andrew O'Neill said, they render a lot of detail
* They easily (far more easily!!) build density, which is nice in a gumover as gum really takes either a lot of layers (and a lot of work) to build serious density, or you have to apply a ridiculously high-contrast layer which in my experience tends to create a very coarse/grainy image which is not always pleasing
* I didn't do many gums, but in that limited experience, the process would become more and more challenging as you build up layers; anything beyond 3 layers for me became challenging quite quickly, partly due to registration and warping of the paper, but to a large part also due to adhesion problems with subsequent layers. I'm sure more experienced printers more easily/aptly deal with this, but I also wouldn't be surprised also for them it gets more challenging as layers build.
So in short, I think cyanotype is a very effective first layer to use indeed, in many respects.
That's one of the beautiful things of gum printing; you have quite a lot of liberty in determining the contrast of each layer, so rather complex multiple splits are feasible.