Granted, but we don't have the abilities in game that fighters would have in real life. Also angles are much more important in real life. Axes can't hook shields, horsemen at full galloping with heavy weapons can all be taken easily by a really weak shield stance (and a really crappy shield), you can't attack the legs of a shield bearer (with a sword). Even if low tier soldier might realistically hide behind shield, experienced soldiers should have a good counter one on one (I find the kicks pretty lame, the hilt smash is a little better, typically they can recover and get the shield in the way quicker than you can strike though).I use Realistic Battle Mod which makes the AI even more defensive, and yes, I do find it annoying when a low tier enemy turtles behind his shield when all I want to do is quickly kill him so I can get to where I'm going. But c'mon, that is exactly what a scared soldier would do.
Battlefields are not the place for duels. As said, flanking is the best way to tear apart your enemy foot soldiers. And quite frankly I wish the soldiers would be even more defensive. Even with Realistic Battle Mod I don't have time to attempt maneuvers. I'm trying a Cav-less Sturgian army this round, and I would love if I could use my line-breakers effectively to either flank or to... well... break the line. But then I'd need some shielders to protect them from the enemy ranged, plus split my regular troops into two, three or maybe four divisions so I can either spread them out or pull back, plus have a reserve which I could use to add men to flagging divisions.
But this will never happen. In real life two equally sized battle lines could fight for hours until exhaustion set in. A soldiers first and main priority was staying alive. Spears kept everyone a healthy distance away from each other, and the shields were never ever lowered. Now I'm not saying every battle should last several hours, but even if you had two equal armies fighting face to face with no flanking or any tactics it should at least last ten minutes.
So I say lets make AI even more defensive, and give recruits shields. It's odd that the worst soldiers would not have one of the cheapest pieces of equipment to produce.
I don't mind the AI using shields to help their defence, I just wish it the shields strength came from how they used them and the shield itself, rather than just being unreasonably strong. Right now, the only thing prolonging battles and giving troops survivability is that all melee troops are equally awful at killing each other - it'd be nice to get a more dynamic balance where slightly tipping the scales can lead to disaster for one side; good incentive to plan well, know your troops and keep a well-balanced party.
But I get what you mean about making AI more defensive, they're not very smart at the moment. I'd be all up for that, I only think the shield itself is OP but the man behind it is dumb as rocks: basically, I'm annoyed because the dumbass only lasted so long because of his deus ex machina shield rather than his actual strength or skill. (Some of my custom troop mods gave shields to the recruit unit and they perform so much better than regular recruits, which at the moment are basically just free kills unless you get mobbed).