I've been playtesting mounted combat with my players and have some issues with its feel. This is especially problematic as one of my players is a bit of a stickler for "realistic" fighting; he knows a lot about medieval combat. Usually I'm able to explain it away with a little DM flavoring and explanation that it still needs to be a functional game. However, mounted combat feels really wrong. Instead of charging valiantly in with a horse you end up just getting a movement bonus and/or a free disengage. The combat ends up feeling very stilted, not flowing at all. This player in particular is kind of outraged at how ridiculous it is that a lance is just as effective whether you are standing still on a mount or galloping in on your target. I was wondering if there was some way I could alter the rules that wouldn't break the game. Is there already a ruleset out there that deals with this?
It is important to understand why the Mounted Combat rules feel so clunky; which is to mostly blame on the fact that when you are controlling a mount you can only do 3 things; otherwise the mount acts on its own and with no direction and can use any number of abilities and/or attack options it has.
This was done on purpose so that Paladin and other classes who can summon a mount for nearly free do not see any significant power spike.
How can you re-balance this if you believe the rules are unforgiving and less realistic than preferred?
Try integrating the Mounted Combatant Feat
On page 168 of the PHB it gives details on a feat called 'Mounted Combatant'. If you so desire, you can grant anyone using a mount these passive abilities to simulate the expertise and training it would require to actually be a formidable opponent on a mount if you think their character would have such training....because just jumping on a horse shouldn't mean you can use a lance more effectively from upon it.
This player in particular is kind of outraged at how ridiculous it is that a lance is just as effective whether you are standing still on a mount or galloping in on your target.
True, the rules for Lances in the Special Weapons section of the PHB says a Lance requires 2 hands to wield when you aren't mounted, which means standing still on a mount or otherwise; but you can make simple changes to address that. Make that special property only work if the mount moves at least 10 or 15 feet first before the player attacks. Alternatively you could give the Lance an extra damage die if the mount takes the Dash action and moves before the character attacks with it. Among other options you might be able to come up with.
D&D is a lot of things, but a combat simulator is not one of them. The Developers do their best at it, but applying realism and trying to intellectualize or analyze the fantastical elements of a fantasy role playing game becomes tricky. So when there is a demand for such a thing, we just have to take existing rules and alter them a bit to suit our needs knowing that; every time we do, we risk potentially upsetting the balance and power of things.