All known -- and all too frequently disregarded; often for inane or insane reasons.

Obviously, own unit quality has an effect on casualties and all other factors of warfare. The vagaries of that fact are a principal cause of the military propensity for overstrength and perhaps excessive redundancy. Regrettably, legislature, bureaucracies and poor leaders refuse to accept or understand that with obvious failures attributable to that refusal.

As a point of minor interest, I don't believe that the Selective Service issue, the Draft, contributed heavily if at all to a lack of unit cohesion not only in the 7th ID up north but in that Army in Korea as an entity. The KATUSA program was definitely an adverse impactor and a detriment to unit capability and performance (one the Marines refused to accept due to that fact regardless of the political desirability and the practical benefits to the Koreans) but poor Army personnel and training policies of the day contributed far more heavily to unit failures in Korea than did the Draft.

Those personnel and training policies are a little better today still leave quite a bit to be desired...

I'm not at all sure that there's a decent solution to the problem of maintaining unit cohesion over the long term. Good or better cohesion will not always be possible but I believe it could be achieved far more often than not if units were properly organized, equipped and trained and if they were properly led -- and employed. That not least by the political leadership who do not do the employment thing well and who would not like the costs of such units...

We are stuck with the simple fact that good units develop and maintain unit cohesion under adverse conditions. The solution is to simply have more good units and that can be done by more selective recruiting followed by more effective training and by better selection of Commanders. Not really that hard -- but very difficult in an egalitarian democracy that is perhaps overly concerned with 'fairness.'