I agree with you in many ways, especially about the fact that some manufacturers write that their devices give out a power of 1500 amperes, while the cable section is designed for a maximum of 150-200 amperes! And even with this power they quickly fail, melt)). But what I disagree with is that you cannot start without a regular battery! I started an old American Corvette without a standard battery. Engine displacement 5.7 L. Start with a JIC T-800 starter-charger. The difference is that good, high-quality launchers cost not 3 or 7 thousand, but at least 10 thousand.
We know. ) We also know that the engine will help start a 14-volt battery from a screwdriver, connected in parallel with the standard car battery. Sellers of "launchers" with lithium-ion batteries are a little cunning when they indicate the starting current as much as 1200 amperes. But at the same time, the cross-section of the wires with which these "launchers" are completed will simply evaporate at such a current. The thing is that a discharged car battery needs very little help to start the engine. If it is discharged "to zero", or there is a desire to experiment with starting the engine only from the "launcher" with disconnecting the standard battery, then nothing will work. And the sellers are silent about the fact that the launcher lying in the trunk in the winter and supposedly charged is absolutely useless when starting the engine. "Puskach" loves warmth!