Oh, it was a very real plan. With hundreds of armored vehicles on the way, helicopters with elite russian forces landing in Hostomel airport, semi-surrounding Kyiv and so on. The plan largely depended on Ukraine not mounting effective defense and surrendering in shock.
Ukraine has a very effective artillerie, which with west supplied arms gets even better. The problem is quantities, with russia having tons of old deadly junk to throw and west arms coming in too slow.
You might be partially right, Russian military bloggers state this version too. Like there were tons of money invested into bribing Ukrainian political forces but it was stolen on both sides.
However, right before retreat Russians were not in a disasterous state at the borders of Kyiv. In fact they were slowly closing the circle around it. If the focus were there, and additional forces were applied, it could have succeeded.
Russians had heavy losses during deployments, but once positions were taken it all stabilised for them, so it was not as disasterous as many say. It was not that Ukrainian forces pushed Russians back, but more like Russians regrouped.
From what I see in the last weeks, Ukrainian artillery is not capable of achieving goals. It could have been different before, but now a lot of videos from Ukrainian brigades depict that artillery support is missing and they go to battles without any support.
Ukraine has a very effective artillerie, which with west supplied arms gets even better. The problem is quantities, with russia having tons of old deadly junk to throw and west arms coming in too slow.