That opens up another problem that I've seen talked about. The air that is left at the end. So for a mass driver to work, it needs to be close to a vacuum, otherwise you've got all the air in the way. Another reason the Moon is so easy. So when the payload that we can send through this ultimate roller coaster gets to the end at the top (wherever the top is), how do you manage an airlock there? It can't be open long, otherwise the thin air will start filling the tube and be a barrier to run into, but it can't open at the last millisecond because what if it doesn't open fast enough (for whatever reason)? Plus, if it got through the airlock, it's still going to run into the thin air outside, which will be like hitting a sudden brick wall at that speed.

I've loved the idea of mass drivers since I was a kid in the 70s dreaming of space colonies. But there are some serious problems to overcome on a 1 G planet with an atmosphere.

As far as the mechanisms of the mass driver itself and the power, I think that's doable even for large loads. It just doesn't work for other reasons. The opposite of a mass driver is an electromagnetic drive and we do that in limited fashion on some trains and other places. They would also be an awesome low acceleration drive for something like asteroid movement, using the slugs of mass on the body itself to change its vectors. Although that bears the Mass Effect warning about shooting without a target, it will ruin someone's day one day.

To make something able to handle higher g forces you must make it heavier, if it is heavier you require more fuel and launch power to get it to orbit. Mass drivers for orbit are of fairly dubious utility, especially for all but very compact very dense payloads. Being higher altitude at launch is of even more dubious utility for rocket launches, very little of a rockets energy is spent gaining altitude against gravity, as all fuel used fighting gravity is wasted. The bulk of a rockets thrust is used accelerating the rocket to orbital velocity. Even airplane launched rockets see limited use. For reference, the delta v (a measurement of how much a rocket can change the velocity of its payload) budget for low earth orbit is generally 9,300 to 10,000 m/s, the orbital velocity there is about 7,800 m/s. We're talking about a fairly small fraction of a rockets ability saved before we figure in the expense and risk with making your payload and stages so much stronger and risking your delicate and typically much more expensive than the rocket payload with a much more physically violent launch. And the first chunk of a rocket launch is when you burn off a ton of the fuel while the rocket doesn't get that much lighter relatively speaking, you're mostly paying for fuel at that part of the process, and the fuel is far and away the cheapest part of a rocket.

Also had another thought on that pesky air in the way. Something related to your point is called Max q and occurs very high up still in the atmosphere, even above most of the air, because of the speed also involved. The advantage of a rocket is that they can manage the ratio by backing off the throttle until getting past that point. But important to this conversation is how high that occurs. Even if the mass driving avoids the lower air, it still has to come out of the tube at a comparable speed to attain orbit, so it will run into its own Max q type effects as it exits, and then even further up. The stress on a vehicle would certainly be far greater than "just" a rocket launch.