Magnuson-Moss exists to prevent warranty cancellation when a customer uses an "equal" but not OEM supplied part.
I’ll elaborate only a little, because the explanation and previous assertions from you - and from me, were overly simplistic.
MM doesn’t simply protect you from a manufacturer denying warranty coverage for non OEM consumable use, it protects you from shady dealers, and cheaply made or engineered vehicles, when the vehicle starts to exhibit higher than normal failure rates and the regional reps start driving efforts to ‘find a reason- any reason’ to deny warranty coverage. As you previously alluded to in another thread about denying a warranty claim for an obvious incidental modification.
This does happen in varying forms. The RR in my lawsuit was present at every service I had form the time the legal papers dropped. My paid witness and one of the mechanics at a dealer caught him saying exactly this and it became part of the suit. At one of the numerous strandings and subsequent repairs he and the corp counsel kept asking the mechanic over and over if what he found was abuse. It was comical and stupid, and after the 3rd or 4th time the mechanic told them to get lost, got the service manager and had them removed, leaving my team. That was a busted fusable link. it just popped, the truck went dead on the highway. Only 3 days down for that repair.
MM insulates you from bad actor “policies" - which you’ve indicated largely come from the dealer side - mech., S/A or S/M giving the blanket ‘abuse’ declaration or warranty voided because of some incidental mod. That kind of stuff is stupidity on a grand scale, but again it happens. If your service department is fishing for a reason to deny your warranty coverage, MM can protect you in some cases. We’ve practically all been victimized by something similar at some point.
Now, things are vastly different. Most dealers value the customer service feedback and actively solicit you to give online reviews and what not. This is rapidly becoming a pretty good tool to use for both good and bad experiences. It used to be if you got a bad experience from the dealer, you were SOL. Now, you can actually drive business away just by being honest on the internet. I think this, and not lawsuits, is the death knell of the alpha hotel service manager or service advisor. Online comments like “I’d go there but the service manager yelled at me and made me feel dumb” goes a long way to driving business elsewhere.
I’ll just close with pointing out that corporate counsel for auto manufacturers who represent manufacturers in lemon law suits are sub-atomic goo not even rising to the level of pond scum. I’d call them the lowest form of life known to man, but that’s being too generous.