I posed the question on the AdG forum, and received a very good reply. Take out the AdG-specific stuff and you should still have a useful strategy to use in other systems…
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"So having run Gauls and other mostly HI impetuous armies. It is not as completely forlorn.
Madaxemen posted this versus a German foe
link
The German list he opposed is pretty close to a Frankish in options.
The issue of "getting to the flanks" really requires a high speed army doing it on turn 1. The HI will be moving as rapidly as possibly into contact. And it is not easy to punch through these HI. In one game I was going to throw 7 Knights at them. Well the enemy wheeled. So I only got 5 KN in cleanly. Essentially the KN are up 1 in the first round and have Armor. So where the KN win they start to grind through. But once the KN lose on a bad die roll, they likely are ground down. So the question is, do the KN get through fast enough, with enough.
The Franks will presumably have tried for a coastal zone to secure one flank and some other terrain too if possible. They will know that most foes will swing to their flank and deploy assuming that. That is what their CV does, delay and evade until the HI can wheel in.
Coastal zone 4 UD + you don't have to deploy next to coast, say 3 more UD + 11 HI, you are now 18 UD covered on a 30 UD board. Of those remaining 12 UD you have 3 MC and LI that mean no one is double moving. That is if there is no other terrain of significance. The big HI command can be deployed at an angle as the 3rd Corps. So it is part way into its wheel with a secure flank. Sooner or later the enemy will meet some portion of the HI head on and have to try to bust through. Without KN or EL that is an even proposition at best.
Personally I like Gauls more than Franks. But what is great about ADLG, is these armies actually are viable enough to be worth playing."