It would have been way smarter to train Ukrainian troops in secret on those MBTs and IFVs and when announcing those deliveries, they would have been ready.
This would probably not be possible. It would only work if the West was as united in their support of Ukraine as Russia thinks. In reality these are all democracies with complex internal political debates of their own. Putting it simply, if there was no open, public debate about giving tanks to Ukraine, it wouldn't have happened.