A sufficient dose of whey contains a full dose of leucine, where a sufficient dose of casein does not provide a full dose of HMB, so this comparison is not exactly relevant. Your comparison of HMB and casein would perhaps be more akin to comparing the muscle building effects of, say, whey and creatine, or betaine.
Also, your point about casein’s ability to simulate MPS without influencing insulin is great, I can respect it, but it’s not exactly relevant to the discussion of HMB, as the primary anti-catabolic MoA is HMB is not via increasing MPS, as it is actually quite poor at this relative to leucine.
You still haven’t provided evidence that casein is more anti-catabolic then HMB. Even if, as you say, you don’t need a direct comparative study to prove this, at least show me from where you derive your conclusion. Saying that the anti-catabolic effects of casein are well documented and proven is great, and I’m not disputing that, but this in no way proves that it is superior to HMB, only that it has a similar observable effect. Your claim of why casein is a better anti-catabolic supplement than HMB didn’t even mention HMB, or compare it to casein with any actual evidence/data, but only said that casein’s effects are well known, and somehow acted as if that statement is enough to conclude that it is better than HMB. There’s also cost to factor in in terms of value/best, and a full dose of HMB seems to be cheaper than a full dose of casein.