Okay, so I tried some more and I'm still unable to do it. A few times, I've had enemies walking towards me but the kick still missed. When they're running towards me, they stop too far away.Yep, it does seem like the battle system has been altered a little sometimes in S1, there's a bit more of a challenge I think in some battles, and I've noticed when you've got them by the arm, if you let the enemy move towards you then kick, they'll get a boot to the face, but if you kick, they back off, and you don't connect. On DC I think it's a bit less complicated AI, but I could be totally wrong
I'm not sure how you were able to pull it off so easily. Since you're saying that you've done it, I suppose that means it is possible. But the game still plays differently than it did on the Dreamcast, which to me constitutes a bug. It should be replicating the original game as closely as possible.
If you're able to hook up your DC and play your original copy of the game, I would urge you to do so. Try doing the kick during the same fight in each version, back to back. I guarantee you'll notice a huge difference in the way it plays. When I try on Dreamcast, I'm kicking dudes left and right but I can't seem to land a single one on PS4.