it seems to me you've got a very heavy rim (without eyelets if that matters to you) on a fairly pricey hub
Certainly the Hopes are pricey - but the Archetypes are not significantly heavier than the Open Pros which you recommended. They've a taller stiffer profile, but yes, lack of eyelets is a concern to some - especially if you are a butter-fingers like me and are forever dropping nipples and retrieving them from the box section!
Note that I did not say less spokes makes a wheel 'fragile'
per se. There was a qualifying adjective in my post.
I could just as easily have said "why not opt for a more robust build?"
I agree about balancing up stiffness, comfort, weight, but those are all impacted to a degree by the weight of the rider and the terrain over which the bike is to be ridden. I would add other factors into the equation: durability (which rules out Open Pros for me because brake tracks wear too quickly), ease of getting tyres on and off (which rules out Rigida Chrina, some of the Exal offerings), the tyres you want to use (if wider than 25mm or converting to tubeless I'd rule out the Ambrosio Excellence)
I've built on all of those rims - and based purely on the fact that the OP is talking about replacing a Roubaix (rather than, say, a Tarmac) it seemed appropriate to invite consideration of something other than absolute minimum weight. Maybe too much of an assumption on my part?