I think it hurts some of the cool terrain gameplay if a player can just click the road button to automatically benefit from roads. They should be required to use a roadlayer unit first who does NOT get the movement bonus.
For example, let's say I put down a bunch of forests with the Create Forest spell to slow down my opponent. That's cool! He's a materium dork and he counters by building roads through it. Also cool. However, even his roadbuilder benefits from the road move bonus, which makes the forests a bit pointless. He should have to slog through the forests to build his roads, then everybody behind that first roadlayer should benefit.
TLDR: Having the roadlayer benefit from their own roads hurts the cool terrain gameplay of AOW4 and ruins some fun terraform dynamics.