Well, it is a little more complicated because as Mt Everest grew, that is, as the land went higher and higher, at the same time erosion was taking place. So the actual height at any time is the balance between the uplift rate vs the degradation rate by ice, water and mass wastage.

So, here is a nice way to think about it:
Let’s say you start to fill your bathtub but the valve at the bottom leaks a little. Then when you turn the water on the amount of water in the tub will begin to increase, but there is a leak!!! So, if the leak rate is less than the fill rate, the tub WILL accumulate water, but if the leak rate is greater than the fill rate, well the tub will be EMPTY, no matter how long you run the water!

So, the height as a function of geologic time of Mt Everest is the difference between the rate of uplift vs the rate of erosion.

What drives the uplift?
We know that gravity, wind, water, ice, and mass wastage drives the leak. But what drives the input (uplift)?

Uplift is driven by the collision of INDIA with ASIA. These two continents are on separate plates (plate tectonics) and when the plates collide, the stuff has NO WHERE TO GO... so it goes up! Then gravity works against that.

Fantastic question! Mountain don't get pushed up all at once, and then simply begin to erode. Rather, mountains are uplifted and worn away simultaneously. If uplift exceeds the rate of erosion, a mountains slowly gets taller through time. Conversely, if erosion rates are higher than the rate of uplift, mountains become lower. So...Mount Everest continues to get pushed up (since the Indian Plate is continuing its collision with the Asian Plate), but, as you note, wind and water (not to mention gravity, chemical weathering, plus other factors) are working to lower it. Nobody knows how high Mount Everest might have been in the past, but there are good theoretical reasons to think that it was never much higher than it is today. One factor to consider is that the bigger and heavier Mount Everest becomes, the more it's root sinks into the less solid interior of Earth. A good analogy is stacking bricks onto a trampoline. The more bricks you stack onto a trampoline, the further that pile of brick that you're building sinks into the trampoline. With time, the top of brick pile doesn't necessarily get higher as you continue to add bricks, because as the weight of the pile goes up, so does the amount of sagging.

Bottom line--the height (and shape) of mountains reflect the relative rates of uplift and erosion--the elevation of mountains is never steady over geologically significant spans of time.

Mt. Everest is actually growing and not eroding! As tectonic plates push together, it pushes the mountain up higher than even before. Erosion happens so slowly that Mt. Everest is actually still getting higher rather than shorter.

Mt. Everest (and any other mountain) is in a constant battle between erosion and geological uplift that creates mountains in the first place. The uplift is still pushing the mountain up as erosion bring it down. There are also faults that the different rock formations that make up the mountain can slide past each-other along. I do not know which of these forces is currently winning, if Mt. Everest is getting shorter, or if it is still growing.