Red dot serves 4-5 purposes (at least).
1. If a threat pops up very close while you’re on 8x, it’s WAY faster to rotate slightly and engage with an offset red dot.
2. An offset red dot is WAY better than iron sights as a backup sighting system if your primary is compromised by fog, mud, or damage.
3. An offset red dot is WAY better/faster than the 1-8 for passive night vision use.
4. When on 8x, if you’re not immediately finding your target in your (small) FOV, rotating to the red dot, and rotating back after you’re on target, is WAY faster than other known methods.
5. When using a clip-on (NV or thermal) it’s WAY faster to rotate and use the red dot if a threat is close and requires white light.
And on and on and on.
If you’re a paper shooter (nothing wrong with that), there’s probably no advantage.
Why not pair a 4-16 with the red dot?…
Some of the previous does apply. But the 4-16 will be much heavier. The objective will get at least partially in the field of view of the red dot.
Additionally, most people find a 1-8 on 1x to be faster than an offset red dot, so you’re giving up speed.
If you have a clip on (NV or thermal) you’re giving up significant speed/resolution by going with a 4x bottom end instead of a 1x.