Part of DND/CAF's problems is the intersection of the two. EPMs should not be military. ADMs, which are departmental, not CAF, should not have 2* Chiefs of Staff merely to give some poor branches a "thanks for coming out" GOFO position.
Lots of organizations in DND do need military expertise for input, but bureaucratic expertise to advance the requirements. A rotating cast of military personnel slows progress immeasurably - you either get "the streamer posted in for a year to get a tick in the box who never understands it who causes more harm than good by trying to leave his mark" or "Bottom of the bottom third abandoned for years and ignored by peers".
In trying to do too much of the Departmental administration, the CAF loses focus and starts to adopt damaging, MBA type mindsets.
For example: the CAF needs cooks who can plan and execute balanced meal plans based on available ingredients. Thus every base was different, and the senior cooks got the experience they need for when they deploy. Today, instead, we've adopted a national standardized menu. More efficient (less costly), but our cooks no longer practice their necessary skills for operational employment. Or the tale that at a Qualification Standard writing board, an airfield engineer was adamant that they could cut all that useless airfield battle damage repair material, because they never did it in their day to day work.
The CAF focus needs to be on delivering military capability to meet the needs of the government; the DND focus needs to be on managing the systems to support that. When the CAF has too many managerial jobs, those behaviours become incentivized, to the detriment of the CAF.
On the flip side, a bunch of defence scientists in the US set the performance requirements for one of the recent generation of US kevlar helmets. Ballistic requirements, comfort for extended wear, etc were all based on state of the art knowledge at the time. Bunch of prototypes were built, did great at stopping bullets and every single one of them broke during the field testing, because no one thought to consider the normal things the troops were used to doing with the helmets like use them as improptu seats.
Our ADM(Mat) orgs are a mix of civvie and military; you get the mix of people who have actually used them for practical considerations, and you also get some outside ideas coming in for different ways to do things. That helps us usually avoid things not being fit for purpose because we didn't think of how they may actually be used (outside what a textbook says).
Generally speaking I can't really think of any streamers that just bounced in and out of MEPM; there are plenty of high profile jobs there, but it's also recognized that you need that continuity, so postings of 2-3 years is the norm (with some extending longer if it makes sense). On the technical support side (for the Navy anyway), there is a lot of work between the EPM and the formations to keep things together, so having people with experience on both sides is really important, and something we would lose if it was all military. Also gives us flexibility to put extra horsepower into critical areas as required and re-role people easily, so having a uniform doing effectively a civilian job is a big advantage when you are putting out fires (and we're cheaper for the SWE). There is a lot of politics to moving civvies around that you just don't have with military, so gives us a bit of agility that we wouldn't have otherwise.
Agree with the MBA approach having problems, and the other issues, but it's not really a simple all/nothing approach, and there's a lot of stupid things we do, (like give promotion points for 'breadth of experience' that encourages job bouncing) that add to it as well. Maybe if making things run smoothly was equally as valued as 'promoting change' that would kill a lot of the good idea fairy initiatives.
COS Mat is a lot more then what you are making it out to be, and there is a good reason they tend to go into 3* jobs or pull the pin and become an ADM. I'm not sure who the last ADM(Mat) without time in uniform, but when they are responsible for every single bit of kit in the CAF, just makes sense to maintain that civilian/military mix throughout the whole organization. If nothing else people in uniform is a very easy way to remind people that they aren't just buying widgets, and makes sure there is a small pool of people that could step into the role with confidence. It's an absolutely critical job, and if you think our procurement record and funding levels are bad now, just imagine if we had a less then stellar ADM that was getting pushed around by TBS and others.