The problem with ramjets is that below the realm of about mach 3 they are inefficent. Below mach they are terribly inefficent. This is simply due to the low inlet air pressure at which they are operating. You can see how large the test one on the Dornier is. This is because volume and more fuel can make up to some degree the inefficency of low speed ramjets.
When I discussed these earlier I was infering that this inefficency was understood as a general principle and that any sort of aircraft that was going to use ramjet propulsion would have to rely on some other means of acceleration to a fairly high speed before starting its ramjet.
One only need look at how rare operational ramjets are in aircraft today. Between their inefficency at low speeds and their difficulty in being started to begin with (ie the requirement for an alternative means of acceleration) one can see that the whole concept is really not practical in an operational military aircraft.

Yes, the Germans were well ahead of the Allies in general in supersonic wind tunnels both in their theoretical design and their practical application. This did not however translate into any sort of useful military applications duing WW 2. This is simply a case of German engineers having exceeded the level of practical application and then not having been checked by operational need.
Essentially what I am saying is that experimentation on the edge of technological possibility in a wartime setting, especially one where you know (or should know) that you are an industrial underdog is really, really stupid. It is far better to quickly and ruthlessly concentrate your efforts on key extant technologies to win NOW against a logistically superior opponet.
This is exactly what the Soviets did. They pared their industrial output down to essentials and little else. They sought victory through quantity not quality. And, they succeeded brilliantly.