We can use walker for that then. I'm less sure of the others. How about this:
Base: Leader and Invulnerable
Offense: Character Sniper, Inspiring and

?
Defensive: Leader and Thick Rear Armor
Utility: Walker and Invulnerable
Offensive: I don't think we should change a core action so much as such no movement when sustaining. Actually, due to the nature of sustain (no movment) it's always felt a bit more defensive due to the movement restriction. I also don't think we need to give the entire formation sniper. It should be enough just to give it to the character's unit. There's potential for sniper baneblades, shadowswords, valdors, and russes. All have powerful weapons and can easily neutralize whatever unit they decided to put the attack on. A whole formation of that seems a bit silly.
I'd also like to see the leader function come through a bit more sparingly. We need trade offs too not just outright bonuses. Leader is a perfect example. You can hit harder but without leader you are easier to suppress. Hopefully it makes a player think more about what he takes rather than just using whatever gives the most raw firepower.
The biggest issue I see is that with the existing specialist options there just aren't any that work as offensive options and don't overlap existing weapons. Most of the means by which we can make the unit more attack oriented also seem too over the top or change core rules I'd rather not mess with.
eg. Remove the -1 penalty for doubling and allow units to fire with -1 when tripling would be a nice boost offensively but at the same time it modifies two core actions and makes the standard move redundant. Allowing a +1 to hit is also a nice option, but it interferes with the sustain action. Giving them things like First Strike also seems a bit odd since most of the units have poor FF and CC capability. Extra attacks seems like it could work, but again it's a bit counter-intuitive since the list is weak in CC and FF and granting EA encourages assaults.