Sure, but you can't pull down shields with axes and shields cover areas they shouldn't be covering in the game already. They need fixing first before we can even consider adding new features to them. So saying ''just hit em where the shield isn't covering them bro'' seems kinda silly when, in order to do that, you basically need to John Rambo around the shield wall and hit people from the side (a totally valid tactic, but if we're arguing realism, then also a big fat lol). The spears overhead stab also barely works and is a pain to use over top of a man with a shield in the game. It doesn't work as fluently as you're proposing it does, or even remotely close to it.
I believe shields should be a great tool for defending against arrows and should be a tool used for defending against other infantry. That 2h axes do extra damage versus shields is not necessarily realistic but it does balance the game and prevent people from just sword-n-boarding without a counter to it. And most people, myself included, would rather play a balanced game over a realistic game. Or.. perhaps I should say, my enjoyment of the game should not come at the cost of realism just because someone is upset that ''shields were not used this way in real life!''
I definitely agree that shields are as awesome as you're making them out to be but jesus christ dude, it's a game. Games are not 100% about realism, games are about gamey mechanics too, and that includes balancing shields to be broken by axes/missiles sticking into them.
EDIT: of course, if it was made more possible to strike around/over shields, I see no reason why we'd need to nerf them. But if you are 100% sure that it's already easy to do so, just git gud, please upload a video of you doing it, since I think that would be rather valuable information.