Even a single player can fully restore a factory in 30 minutes.
Seems about right to me, since a single player can inflict the damage in about the same time. And if coordinated with other players who attack bases when the strat goes down, the total resupply time would be much longer than the time it takes to restore the strat. Such coordination might be considered, "strategic".
IMO resupply is the most boring aspect of the game, (and I've done plenty of it). With low numbers taking even one player out of combat diminishes the game experience for everyone, IMO. If there is any role for AI, it is resupply.