Drones have a problem. The reason they're so effective right now is because they're dirt cheap. A $10,000 drone can take out a $10,000,000 tank. And it gets into the issue of how money isn't stuff. Because that $10,000 drone isn't made of much and can be easily pumped out pretty quickly, whereas that tank involved a massive amount of supplies. Even if you have all the money in the world, this is a losing battle.
But as you try to make more sophisticated drones, to the point of aiming to fully replace men on the front, they start to become more and more expensive. You want them to be resistant to electronic warfare and you probably don't want to rely on fiber optics so you need some sort of fully autonomous processing unit on board, capable of generalized scenario processing. And you want them to be able to fly for a really long time, so you don't have to have deployment points front close to the front. And so on. You are gradually just reinventing the MQ-9 Reapers and their $30million+ price tag. And suddenly you've lost all the benefit of drones.
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Russia started peace negotiations with Ukraine 4 days after invading. If you genuinely expect complete capitulation within 2 weeks, you don't start negotiating for peace after 4 days when the enemy would be in a relative position of strength. For that matter, a lot of their early maneuvers were clearly more performative than military in style, like the endless convoys which looked imposing but served no purpose and imposed logistical issues that Russia clearly was not prepared to deal with.
In reality I think Russia did expect there was a high probability that Ukraine would rapidly agree to a settlement, and absent Western involvement that probably would have been correct. And similarly I think the US was probably expecting that Russian forces would just scatter and run at the first sight of Western arms. In reality the optimistic view of both sides ended up not panning and so everybody ended up with a much more real war than they probably expected.