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That is generally correct and it is also correct that radar alimeters don't work so well in areas with ground clutter.

The measurement error in an aircraft barometric altimeter system does not have the necessary accuracy to provide reliable enough altitude info for a helo to fly through a flight corridor that intersects the final approach of commercial airline traffic in busy Class B airspace at or around the 300 level regardless of whether it is AGL or MSL.

One possible contributing factor to the mishap seems to be that the helo was flying through what amounts to a VFR flight corridor under an approach path under VFR flight rules using night vision equipment that makes it very hard to operate under VFR.

The simple solution to this would have been to schedule the night training opps later in the evening when commercial traffic had thinned out and ATC controller work load had become much reduced to reduce the chance of mid air.

The mid air occured at 8:47pm which still a high traffic density time at that airport.

One possible contributing factor to the mishap seems to be that the helo was flying through what amounts to a VFR flight corridor under an approach path under VFR flight rules using night vision equipment that makes it very hard to operate under VFR.

The phrase "possible contributing factor" is understated, but you're on the right track.

The fact that Route 4 went anywhere near the normal glide path for runway 33 is the entire root of the problem. And it appears, since there were two other incidents in the previous week with helicopters, that everyone locally familiar should have known what an enormous, unacceptable safety issue the basic construction of the airspace presented.

All the finger-pointing at dead people is useful on one level, but the basic premise for the entire episode that led to 67 deaths was 100 percent avoidable with sensible airspace structure that didn't deliberately allow the possibility of VFR route traffic in the normal approach path of ANY runway in busy airspace. It's just common sense to see the glaringly obvious hazard - that safety depended more on the "big sky" theory of probabilities than actual preventative measures.

The simple solution to this would have been to schedule the night training opps later in the evening when commercial traffic had thinned out and ATC controller work load had become much reduced to reduce the chance of mid air.

This!