I'm in agreeance on that. It fits more with the direction Fire Emblem has gone with recruitment. In the GBA titles it was common to recruit units from the enemy forces who had little to no ties to your units. Recruiting troops that way, then giving them a cadre of troops would feel odd. But in the most recent Fire Emblems, new units are just given to you during chapters. If Three Houses follows this formula, then it wouldn't be out of the ordinary for new units to join you with their own group of troops already under their command.
As an aside, I do miss the recruitment from the old games. Recruiting enemy generals, mercenaries, soldiers, and thieves was a lot of fun. It added an extra layer of difficulty on the maps, and you were forced to actually earn your troops. I don't like that new units are just given to you like how Awakening and Fates has done it. But with the addition of soldiers serving under each unit, I fear we're going to continue in that direction. Unless by convincing an enemy unit, we also convince all of their troops to defect, I don't see this method of recruitment returning in this title.