It’s lonely at the top of the huge-horsepower food chain. Think about the segment the 2021 Mercedes-AMG GLS 63 competes in: over 600 horsepower, top-shelf, 3-row SUVs: There’s no other vehicle in it. BMW does not make an X7M, Audi does not build an RS Q7. The Porsche Cayenne Turbo has but two rows. Cullinan? Bentayga? Urus? 2-row, 2-row, only 2 rows. Cadillac doesn’t make an Escalade-V, nor does Lincoln sell a Navigator with over 600 horsepower, though Hennessey makes and sells the 600-hp Navigator HPE600. The Tesla Model X P100D is the closest competitor both in terms of power and price, but I’ve driven both SUVs and philosophically they are worlds apart. The GLS 63 stands apart from this crowd.