The press and bench have much overlapping musculature, too. Maybe we should just squat and press, or squat and bench?
The truth is the answer to the question isn't as simple as my first line above suggests, but the lifts that best fit our four basic criteria:
1. Use the most muscle mass
2. Over the longest effective ROM
3. In a way that uses the most weight
4. And thus allow us to get stronger (which, I could argue, includes the reasons why we press instead of push press, for example - it needs to emphasize certain muscles/areas/joint actions in a way that allows increases in force production of those places)
are the squat, press, deadlift, and bench press.
We could also discuss how the DL emphasizes different areas within the broader areas that the squat also hits. For example while both cover quads, posterior chain, and low back, the DL hits the hamstrings and low back harder, whereas the squat hits the quads and adductors harder, even though both hit both pretty well.
For a competitive olympic lifter, the DL may ultimately be an assistance lift for the clean, albeit a very important one, at least until that lifter's DL is already very strong. But for most people for whom strength is the goal, it's not an assistance lift for the clean, but important in and of itself for the reasons above.