Our technology stack is very gRPC friendly, so developer experience is actually better with it, than without (though this is very subjective.)
As for the middleboxes, using gRPC-WEB[1] allowed us to switch Desktop Client App to gRPC even behind firewalls/IDSes that do not speak HTTP/2 yet.
As for the HAProxy, Dropbox used to use (circa 2013) it specifically for loadbalancing, but we eventually replaced it with our Golang proxy. That said, recent HAProxy improvements (v2.0+) make it quite an awesome dataplane and an excellent loadbalancer!