At one of our airports, the service provider wants to get rid of the markers. Cost too much. Replace them with DME-GS checks. Perhaps this is not a good idea. As happened to this crew, under high workload (falsely caused by the premature capture of the glideslope and subsequent stuffing down of the nose to follow the (false) glideslope), a crew could miss the GS check if it's based on DME. Done it myself. A marker beeping and flashing at you is much more likely to get your attention.
I think you're ignoring a key point made in the video (part 2). A single GS check close to intercept point is not sufficient to determine if the aircraft is following an erroneous glideslope. The autopilot may pitch the aircraft down and establish an approximate rate of descent, and then make adjustments to that rate of descent based on the glideslope deviation. If there is no indicated deviation because the glideslope is erroneous, it makes no correction.
With a single OM, the altitude may be approximately correct, even with an erroneous glideslope. But the crew may never live to check the altitude at the MM. With a DME, altitude cross-checks can occur periodically along the glidepath, e.g. every mile.