Don't forget that cover and visibility also affects the mage - not only with indirect spells. So generally the mage will throw a lot less dice than the samurai.
No. Visibility affects both samurai and mage (though the samurai might have better vision). Both their targets get to add cover. The mage might take background count, but the samurai has to deal with attacking from cover and range modifiers also, but gets a smartlink. Both benefit from augmentations and foci.
Generally, Willpower tends to be lower than Reaction, especially against augmented opponents.
The real kicker is that while most targets taking incoming fire will go full defense, they have no defense options vs spells unless counterspelling is available.
Overall, the mage typically has an easier time hitting, can hit a lot of targets, and they can't soak, but only 1 attack per IP and counterspelling really screws with them.