There are a couple great mage staffs out there that I've seen (and I assume I have not seen them all), that add mana and/or spell damage boost. Should a mage also get a powerful, no-init ranged weapon on top of all they already get? I'm not so sure they should, and here's why: Every ability that allows you to do risk-free damage has a high cost, whether that's the magic costs or the init modifier on a bow/staff (which your suggestion for a champ archer build is great, though I'd make it available to both warrior and assassin paths, because the init penalty would go away in stages as you "paid" for it). For their incredible power, mages pay the cost in mana, talents, resist chance (early on), and time gaining/protecting shards. There is no equivalent cost other than that init hit on ranged weapons--so removing that even through several talents might make them too powerful (an "I kill for free" weapon). The more sensible thing to do (and I believe this is the dev's intent) is to use a dagger's high init going into a fight if you intend to cast a lot, and a ranged weapon if you don't intent to cast (or have a melee hero cast haste on the ranged guy as he's running into the fight).
So the question of balance might be this: if you had a buff mage who could also hurl mana-free range damage when he doesn't feel like casting, why would you need/want any other class? I think having to use gear/spells to overcome that init hit is a really good dynamic that should not be removed through talents (because then you'd get these ridiculous high-init ranged champs who were untouchable). Thoughts?
Also, you have to be careful making too many bigger tactical maps, or you discourage melee builds--why make an assassin who has to take 3+ turns getting at a ranged unit, when you can simply have your own ranged units?
On a related note, I built great archer units with about 24 init, and like in the old days of WoM, they mopped up the map (with the exception of that huge group of mercs in the dragon eye quest--their damage soak was just too high for the 3 5-stacks of elite archers I brought to the fight; of course, I could have simply come back with 9-unit stacks and gotten revenge had I felt like it). They seem balanced well and still viable without being overpowered (you have to invest quite a bit into them to get them on par with, say, a group of pikemen, but then you take no losses, risk-free killin').