Let's start off with something that most people will agree to (but maybe not in the form I say). No not servers that's been addressed enough, but a new game mode.
When people refer to medieval wars they always think of charging the gate, breaching the walls, climbing the battlements, penetrating the court, storming the keep, and conquering the throne. It's because of this that I'm truly shocked not to see a siege type of game mode present from the jump. Imagine having a game mode identical to the last chapter of the knights storyline. Opposing team starts off trying to infiltrate the borders of your kingdom by trying to climb the battlements and attacking the gate and walls with siege engines they must protect from your teams counter attacks. If they make it in they must fight to take control of vantage points to force their way through your army into your keep and up to the throne. Here, at the throne, would be where the defending team and their king would face their adversaries for one last earth-shattering elimination style clash of honor where the winner takes all. There should be a timer per phase of the match and the king should be combat able and have stats like the ones from the story mode. This mode could have a second round where the teams switch positions, or because of the duration it could be one round and done. I would recommend the two round match, but either would be great.
Another suggestion that should get viewed fairly well is an optional Realistic gameplay style.
I am one of the many people I know that like hardcore gameplay over core. Do away with the radar, enemy team icons above the head, passive perks, healing on base, and attack indicators. Let us fight a battle where we need to seek out our enemy before they do us. Let us take out as many knight and samurai scum until our last breath (sorry team Viking all the way lol). Increase the damage taken. For us to fight more united and strategically. These random people thrown together separate and find themselves outnumbered are forced to spam moves to keep the enemy at bay or flee in hopes to join up with a comrade. When a mighty army is upon you the strong will stand together and fight them as equals.
My other suggestion will probably get a lot of negative feedback, but it's quite straight forward.
4v4 being the max size is too small. Even in Call of Duty where it's 6v6 people tend to not be able to experience enough gameplay to assuage their hunger for blood before the match is over. A lot of people are just actually getting into the match ( I don't mean joining the session but getting into the feel of the match and opponents) when the match is almost over. If you enlarged the maps and made increased the player base, maybe not to battlefields' 32v32 though that would be nice, people would have the chance to not only get into the feel but get in it and play. I know people are going to say "Making teams and maps bigger doesn't do anything for the length of a match.", but it does actually, because when a game has more players it needs longer matches with higher scores for winning to stay in ratio with smaller games. Could you imagine playing with a platoon of teammates fighting over not three but five bases?
And finally the one most people will probably hate, the nail in my own coffin... the ARCHER CLASS
I first posted this idea in a club on Xbox and it immediately got called dumb. It wasn't called dumb for any logical reason, just that this isn't a shooter game it's a brawler. I of course am fully aware of that, but still label it a war game above all else. War games should have their full arsenal capable of playing. But besides my outlook on that there is more to why I think they should be implemented. Archers, or bowman depending on what you want to call them, weren't all just people who stood back and shot arrows from afar. There is a reason why we see them in comic books and movies using their bows as melee weapons. It's because it was a true way to fight that goes back centuries. Archers didn't just give up when the enemy got too close. Different cultures added different attachments to their bows in case of a close quarter combat situation. Granted most archers carried a backup sword or some other form of weapon. But that doesn't change that some of them learned to use their bow in a completely different way. Something tells me that that guy wasn't worried about how you would make a ranged class fit in but was actually afraid of the new dynamics which it would bring with it. The game wouldn't change all that much, just they way we play it would. An archer can't curve their arrows no matter how good they are. Sorry but Robin Hood Men in Tights was a fictional movie. That said if you are locked onto the archer you only need to block forward and keep moving. If you're locked onto someone else you block the same way you do now when someone jumps in, they're just further away. When you look at it this way it sounds like the Archers would get a raw deal. It's not true however, archers would have the huge advantage of being able to lock on to their target first, due to their keen eye sight. And being one of the fastest people on the battlefield you would be able to stick and move at a distance to lure the enemy to a location of your desire. Which could be a beautiful ambush. In fact I would say you greatest adversary would be the assassins, who could quickly shorten the distance between you. When both the pros and cons of a class contradict each other it usually means it's a fair class. We will still have to be aware of going under drop spots, but makes us have to pay more attention to your surroundings everywhere else as well. There's two ways to play this one. One, you could give them RB to shoot and RT to swing. Seeing as they aren't melee they would use more energy to hit people and they would want to do it with all their might. Or two, RT to shoot and RB to swing seeing as their shoots would their stronger attack and their melee would be weak (I mean they are archers).
Post Script
Better stat balance between the classes and the races