Modifying Multiclass rules for D&D

One thing that always bugged me about 5e is the multi class and how exp is dished out. When you multi class, you essentially give up a level in your dominant class to branch off. For example, if you're a level 5 fighter (6,500 exp) and want to get a rogue level; you'd have to gain 6,500 (14,000 total) exp to go to level 1. At most, the best your character will be is a Lv. 19 Fighter/Lv. 1 Rogue, if you decide to dump the rest of your exp into Fighter. To me, that's always been a tad much. So, instead I've decided to mod the system a bit, for my campaigns only. Instead, when you gain exp, you can decide where and how much you can put it.

For example, if you're a level 5 fighter and you decide that you want to multiclass, you can put the exp you earned from killing that monster into the new class. So, you're exp bar would look like 6,500/50 as a lv. 5 fighter and a lv. 1 rogue. Then, say you kill a Ghoul, you can either put the 200 exp into your rogue level, into your fighter level, or divide it however you please. This eliminates the limits on how strong your character can get. When you gain a level, you roll the hit die for the class that leveled. Though, keep in mind that the requirements for each class still exist. You can't be a wizard if your wisdom isn't high enough.

Let me know of your thoughts on this modification.

I think there should be a some sort of EXP requirement to start a multi-class at lv1, just so I can't be lv1 at 0 exp in every class.

While I agree that DnD's original multi-class rules are too harsh, I think the way you're putting it is also too loose I guess? At lv10 I can probably sink in a few levels in each class from one or two encounters

Yeah, you have to put some exp into the class before those will apply.

Also, as for equipment and such, the player will start with their primary class when starting. Hit die for resting will be the higher one. For leveling, I think the the class that levels, you can use the hit die for that class.

Anything else you can think of?

To be honest, while this might be fine for the silly tower of d00m thing we're doing, for a normal campaign it's really ridiculous.
It's completely unbalanced and is easy to abuse, with this there's really no reason not to multiclass, which isn't how it should be.
The Handbook version makes sense, you lose some potential power boosts to your main class but gain some versatility from having a 2nd class and having the option to do interesting combinations, multilclassing really shouldn't be required or so good that there's no reason not to do it.

Also let's be honest, almost no one genuinely reaches level 20 playing a normal campaign, and even if they did then they're probably strong enough as is, and even if after that you feel you want to progress beyond 20 there are ways to make that works without breaking the game.

For example, you can continue the levelling chart to 30, and anyone who levels has the choice of either Ability Score Up(Probably allowing them to go past the set 20 limit), or multiclass in accordance to the handbook.

But either way, the point shouldn't normally be about how strong you can get, if that's what you personally want you can have it be that , but ultimately it's a role playing game not a combat simulator. If you make it so combat oriented you're killing half the game.

So basically if it's intentionally set in a Combat Simulator scenario where the players' purpose is to powerlevel and break the game as much as they can then sure I guess this works, but in a normal RP campaign, hell no.