Except that wargear equipment change precisely because of the weapons and defences available at the moment.
Generals don't roll dice and go "herp this century we'll focus on small, fast units of well equiped warriors because we rolled an 11 derp!". They look at the resources available to them, the resources available to the enemy, and try to make the best out of it.
And no matter how much you try to twist facts, no matter how much you keep lying to yourself, it is a fact that metal armor is rendered obsolete only and only when gunpowder weaponry starts being seriously developed. Yes, plate armor was a last-ditch atempt to try to keep up, but when they noticed it, said plate armor was horribly expensive for any kind of mass production, while guns were geting cheaper and deadlier.
Meanwhile a few centuries back the french infantry was basically laughing at the english and their puny arrows thanks to their armor, they just made the big mistake of trying to charge trough a giant mud field. Later on the same war when there was no mud field, the french army was all too happy to charge and rout the english forces in melee.
The even simplier fact that melee was pretty much the main war tactic even when bows and crossbows still existed further shows that, no, they weren't even half as effective at penetrating armor as proper gunpowder weapons.
Short version: Each kind of technology has limits. Both bows and crossbows reached their top state many centuries ago. They couldn't really be improved anymore to any significant degree. Gunpowder revolutionizes everything as a new killing method that had plenty of untapped potential. Gunpowder weapons start showing up more and more, just with a few setbacks, until it ends up completely and absolutely dominating the battlefield.
There's no "ifs" in wargear choices. Generals and troops will pick the best tools available to them to kill and avoid being killed. If an army tries to implement an inneficient tactic with the resources they have at hand, they're butchered by another that makes the efficient choices, plain and simple.
It's not for nothing that we've never seen any real army of unarmed fighters despite all the martial art fanboys that claim the fist is deadlier than any manufactered weapon.
