First I want to say I'm totally okay with the bows having "infinite" range and "infinite" ammo. That's not unrealistic to me in the least for game purposes, but those could indeed be used as factors to limit their power if you want.
Now the base rules don't say the Crossbow can't hit diagonal squares, only that adjacent squares have to be one square minimum between you and the target. When I realized this and started allowing it, the weapon greatly increased in value to the Heroes.
You can make it a lot weaker if you say it can only hit one square away in any direction AND it has to be exactly diagonal (not "Line of Sight" which in the Instructions Manual Drawing is more loose... there's a line that kind of goes around the edge and just barely counts). That's how we USED to use it, before it was pointed out to me that wasn't the intention of the NA edition in print.
I have interpreted it as a pistol crossbow and reloading as a free action (being one handed, it doesn't interfere with Shield use). Some have limited ammo and charged to reload them, I don't do that but you could. Bolts are different than arrows. I did introduce a cheaper bow that's weaker and a stronger and more expensive longbow, but I made both of them two handed while keeping the Crossbow as one handed.
Others have decided all bows should be two handed, and prevent simultaneous shield use (how you handle weapon switching is up to you). You could make it require an action to switch or even go really strict and limit carrying capacity (most don't).
I use black dice to simulate proficiency, so however you handle it, you could say a bow shot with black dice is going to hit more often than with standard white dice. But a green die will HIT less often than white. Pay for archery lessons or give classes a certain thing, or maybe if you post up next to a piece of furniture you get better aim or something? Or coordinated shooting with two archers adjacent or diagonal from each other to hit targets better? Lots of things you could do.
I completely arbitrarily decided that the Mystic (like the Wizard) can't use bows, period, and the Dwarf can't use the Longbow, but the Cleric can.
They say bows require more skill to use than crossbows generally and longbows or warbows require more strength. Various ways you could simulate that if you want to differentiate them further rather than just making them each a replacement for the other.
You can read about my suggestion for "group tactics"
here.