Are 'pushups' considered the ultimate exercise?I'll be honest and break your heart.
There is no ultimate exercise. And if there were, it would be either squats or deadlifts because they are compound lifts that activate multiple and complex chains of muscles from head to toe to achieve an intricate motion.
pushups place tension at the triceps, anterior deltoids, and chest. Core and forearms (and to an extent legs) stabilize the motion. The previously mentioned exercises actively involve these muscles instead of placing isometric pressure.
Ultimately a combination of squats, deadlifts, and bench press/pushups (throw in pullups for added back and arm strength) could take you places.
I personally have a day allocated to a certain muscle group (sunday: chest/ monday: back etc.) Where I do 4 to 6 exercises that active the muscles in different ways.
Fitness is much more complex than to have an all in one "ultimate" exercise.
Happy lifting :)