What makes deadlifts such a good, even essential exercise? To me, it appears inferior in every aspect. Want to train your erector spinae? Do back hyperextension. Want to train you posterior chain? Go for hip thrusts. Quads? Squats. Grip? Hang. All those alternatives are much better, in my mind. Besides, you activate arms and legs at the same time which, it seems to me, may comprise you recovery. Why is it consistently included in must-do lists?
Most of the real-life movements and lifts we do (i.e. not in the gym), are movements where you have to recruit a bunch of different muscles at once.
For instance, when you stand up from your bed, lift something to vacuum under it, or hoist a baby-chair out of a car, you're not just using your erector spinae. You're not just using your hips. You're not just using your grip. You're using all of the above, and then some.
It may seem to be a trivial task, but coordinating all these muscle groups to do their part in the exact right order, to the exact right degree, is something that your central nervous system needs to train.
Compound exercises such as deadlifts, train all those muscles and your ability to coordinate your muscles to contract correctly and as an ensemble - a team even - rather than individually.
This is why you'll find the deadlift as a must-do in almost any strength training regimen.
This is not to say that the exercises you mentioned are worthless. They're all great. And as you do your compound movements, you might spot weaknesses in your ensemble that need to be brought up to speed, and hyperextensions and hip thrusts are key ingredients in keeping their respective muscle groups up-to-date.
The deadlift is one of the simplest and most effective strength exercises. You don't have to do it but it's one of the best.
People consistently recommend the deadlift because it is one ideal combination of simplicity and effectiveness. A friend or written program can recommend this one thing, set a target weight to achieve in some number of months, and trust that with consistent effort the result will be transformative. This is true of only a few treasured movements.
The deadlift is special because it doesn't take much:
- easy to learn
- requires only the most basic general-purpose equipment
- works most of what you want to work
- thus time-efficient
- why do four+ exercises when one does the trick?
- setting goals is straightforward
- e.g. "double bodyweight within one year"
- it obeys "the physics of effort": consistent work over time is clearly rewarded
These qualities make "pick up the barbell" unusually easy to recommend.
The deadlift is special because it gives tremendous return on investment:
- allows some of the heaviest loads
- thus maximum effort
- maximum effort is magical
- has excellent carry-over to most activities & sports
- not true of most substitutes
- nearly impossible to cheat individual reps
- nearly impossible to cheat over time
- you & everyone else can tell
This high return on investment makes the deadlift unusually helpful to recommend.
None of your proposed alternatives are actually superior, just good alternatives. The back extension in particular is an inadequate substitute for the loads possible with the deadlift.
Other exercises which come close to the deadlift in simplicity & effectiveness include running, kettlebell swings, power cleans, presses (from the floor, meaning a power clean too), squats, and pull-ups. But notice that each of these lacks one or more useful properties listed above: a kettlebell or pull-up bar is not as general a tool as the barbell, the power clean & press is harder to learn, squats are easier to cheat or do wrong, the list goes on. The deadlift really is arguably in a class of its own for strength.
I especially like the deadlift because it can't be fooled: it's easy to cheat yourself with most other exercises, doing half reps and or shying away from heavy loads. With the deadlift, there's nowhere to hide.