"Realism" doesn't make a game better, it's just that maybe the last 10-20 years this was what people were trained to believe, how else can you sell a new hardware every other year . Some of the most legendary games are from the 80' and 90' after all.
Anyway correct wall physic is computationally much more expensive, and if you do it with walls why stop there. How about buildings, trees or terrain? You see were this is going. Lag is always much worse then some bending of realism.
Gauls dont seem to have used bows that much until later in gallic wars.
For Cimbrian celtic allies i'd have
Volcae Swordsman
Tigurini (helvetian) Spearman
Maybe also Toygeni (helvetian) slinger if you really want a ranged unit.
EB2 Helvetian spearman
https://europabarbarorum.fandom.com/wiki/Gaisoualos_(Helvetii_Phalanx)