You're 100% right. And I, like most here, don't want to grenade the motor and have a dealer laugh at us when we ask for warranty coverage.
However, we have data to look back on. We're 3 years into Goose having tunes for the Gen 3 and I have yet to see popping motors and warranties being denied. This tells me he knows what he's doing with the tune and it's safe. Yes it's a risk, but the historic data tells me it's a low risk. SO great, FP puts a guarantee on their tune, it makes you feel all warm and toasty inside. Makes you feel good. But really they sold you a guaranteed *************. They took a dump (and a ProCal) in a box and marked it guaranteed. But for my sake, for my daughter's sake, I'll buy a quality tune. Well, I will when Cobb gets the 23s figured out.
And looking at the historical experiences of FP tunes on EcoBoost motors, the warm and toasty feeling of a "warranty" doesn't outweigh the uselessness of the tune.