Falcon 9 is by no means small or even medium. In the history of rockets its quite a large and powerful rocket. And so is Ariane 5. Not sure what you are referencing with Ariane, I guess Ariane 1-4 were small.
So far in history, we didn't have enough to launch. If the volume we launch increases then a larger rocket flying often is helpful.
We are at the peak of what a rocket the size of Falcon 9 can do. If you want full re-usability, the size helps you out quite a bit.
And hauling the 'orbiter' into 'orbit' is only wasteful if you can't reuse it. I would argue what's actually wasteful is throwing the second stage in the ocean, even when it costs minimum 10million $, and likely more.
So far in history, we didn't have enough to launch. If the volume we launch increases then a larger rocket flying often is helpful.
We are at the peak of what a rocket the size of Falcon 9 can do. If you want full re-usability, the size helps you out quite a bit.
And hauling the 'orbiter' into 'orbit' is only wasteful if you can't reuse it. I would argue what's actually wasteful is throwing the second stage in the ocean, even when it costs minimum 10million $, and likely more.