Given that my artistic focus is on musique concrète/abstract composition, and that I primarily work with a small Buchla system, I’ll push aside my usual hesitations about getting into gear discussion - especially since the op was specifically asking about this approach - and throw in my 2 cents:
I do not believe that any particular synthesizer brand or set of modules are inherently more suitable to creating concrete music. If anything, the general approach of this type of music has far more to do about editing (whether on magnetic tape, or computer), and ideas that are discovered from rather limited tools. In other words, when we’re talking about comparing a eurorack system (the one originally mentioned far exceeds the toolset that Pierre Henry had during his lifetime!), Serge, and Buchla, and asking which one might be more suitable for making concrete-style music, the most appropriate, yet possibly discouraging answer is: “yes”
In the photography world, there is a saying that the best camera and lens is the one you have in your hand, and I think the same is true about synthesizers. The more one uses the same set of tools over and over…working through the reoccurring moments of “I can’t do anything else with this thing”…the more one discovers a new approach to using it. I tend to consider the first 3-5 years of using a particular tool as working to get past the obvious.
Now, I do agree that comfort, scale, or style of interface (in particular, the reduction of distraction) can play roles, but there is really very little chance of adequately conveying that experience to someone else through words - everyone is different. What is a comfortable/inspiring scale or layout for me, certainly might not be for someone else. One person comfortably writes with a ballpoint pen, another with an HB pencil. So we come back to the question about which is better for experimental / musique concrète / ambient composition - eurorack, Serge, or Buchla?
“yes…and the one that is already sitting in front of you” 
