Belle Ivers:
The magic of the Deadlands universe is too limited to substitute for non-supernatural technology. It never replaces highly specialized mundane skills (like a surgeon) fully, it never operates on the scale it would need to to create a more fantastic universe, and more importantly most of the population is completely incapable of using magical powers at all.
Surgery isn't a tech skill; so you couls have surgeons
and surgeons using Wonders; development. Also, the population can use/benefit from their local shaman without shamanising, just as they did beforehand. If you ask an earth spirit to landscape a watermill for you, that's not going to benefit just the shaman.
The rest of that is just mechanics in the spiritually-crippled HoE scenario; things have to be that way or they'd have to start thinking hard about the world and it'd shoot off out of genre. Here, post Great Summoning? Should you truly need a message sent faster than a runner relay could take it, grab a shaman or a spirit-powered portal device, go yourself. Send a bird spirit. Visit their dreams Classic-style.
Again, that's because you're tying yourself to a Western idea of what civilisation must be: you're imagining a
Flintstones version of the world, where every present advance is replicated 1:1 in the same order and the same way with different and absurd materials, not an
Über version, where a bit of truly weird advancement sends everything spinning off over
there and causing more research to catch up with the discovery (this still happens even without a war, witness any great breakthrough).
The Great Summoning pretty much bans the Reckoners from the immediate area, but yeah, that's part of the point of the power increase alongside the (manitou)tech ban.