[Twan]

On a map with choke points (like most), or everytime you know where the ennemy will attack, a big yes.

People tend to see these tactics as only possible with static forces but it's ignoring mages have not to start the turn in the province (nor end it there).

If I know your big army is going to one of my provinces I can teleport 7 S mages, enslave half your troops before you can do anything, and use a vortex of returning to bring my mages and slaves back to my capitol lab if I want. As well the fog warriors / rain of stones combo involve air mages probably able to cloud trapeze where you are going to attack.

And, as moves to friendly provinces occur before ennemy moves (another big advantage for the defender), even mages not able to use a movement ritual, can with flying boots be sent to any friendly province in a 3 provinces radius where they will cast first in defence, except if you attack in magic phase.

There is one turn of vulnerability against assassination rituals if you send mages to a non domed province (only if you have not used vortex of returning because you wanted to keep that province), but if your rain of stones killed 50 ennemy casters, or your enslavers took control of half ennemy soldiers, who destroyed the other half, it's usually worth the eventual sacrifice of the 6 or 7 needed mages.

ps : of course some provinces victory conditions may mean the game never reach endgame, or someone can win just fighting indies or sending small forces to a lot of provinces at the same time, making mass spells not worth the effort, but I think this kind of game is an exception more than common rule