Regardless if he's leading or not, Ukraine is the only country standing in the way between Russia and the EU, they are vital to the stability of the continent and must be supported however possible.
Because there's nothing like actual battlefield locations, actual battlefield conditions in some cases, and the experience of guys who recently fought there.
Particularly seeing how the Russians install trenches, minefields, and anti tank defense lines.
Also energy, water, and aviation infrastructure that's still being attacked.
Cause the total training time is smaller when you dont have to transport thousands of soldiers over half the continent. At least the grand of infantry could be trained much faster close to where they already are.
How long is the typical training of a soldier? You are losing 2-4 days to travel, if you are doing it outside of Ukraine. So if we are taking weeks it might matter, but if it's months I doubt those few extra days would matter.