I don’t think Highlander offers anything for Fencers. As a fencer, you get skills that lower enemy pierce resistance while also lowering their crit defense and raising your crit damage. None of Highlanders skills are Pierce, and when you’re done using your skills, you would default to Composee until your cooldowns are off again. Low Rank attack skills don’t scale well (if you’ve seen Rank 8 skills of classes, they don’t even come close), so in most cases you aren’t going to use any of your Highlander skills later in the game. Fencers have Composee and Flanconnade (Pierce and Slash), have no cooldown, and I believe hit twice, though i’m not sure since no skill description explains this.
Barb1 only really offers Helm Chopper for its stun chance, which stun chance on mobs seems like it could be done with Restrain on Swordsman (with aoe ratio equipment and fencer’s naturally high amount of attacks). You’ll have to ask some Fencers with this setup as to how useful Restrain is, but I would hope non-boss monsters can reliably be stunned. At the very minimum, you’d want Barbarian C2 for the second stun in Seism, and the damage boost provided by Warcry (which bringing 10 monsters together would be nice with Peltasta’s Swashbuckling to get the full effect)
No Peltasta means no taunting enemies to bring them to you, no HP bonuses from Swashbuckling’s Attribute, and no Defense/Evasion bonus from Guardian if you ever need to play more defensively, for a party or anything else. I think Peltasta 1 is a must for any 1H+Shield/Dagger Swordsman class.
To me, from what I see from videos, I see Fencer as an Evasion tank class that attacks multiple times quickly and bursts well with a high crit chance (especially since Epee Guard gives you such a high crit damage multiplier it seems from the numbers I see). Sadly, they also seem to live off of mana potions due to the high cost of Composee, and their weapons break a lot due to the multiple hits. I think I’ll just go DEX/CON though the ratio I’m not sure on yet but I’m sure it’ll work regardless.
In any case, what makes you want to take Highlander C3 or Barb C1? Maybe you see something I don’t, but I don’t think Highlander is of much use.