Yeah you’re definitely coming around the 200m slow if you have 21.8 speed.
I’d say you should be getting close to around 23.0 maybe even high 22s and then bringing it home in 25.x
General rule of thumb for 400 pacing is: (200m PR + 1-1.5seconds) + (2 Seconds on top of that formula)
So we get: (21.8 + 1-1.5) = 22.8-23.3 + 24.8-25.3
Range = 47.6 – 48.6
Anywhere in that range would be a big PR for you. Go after it man! 🙂