If it is just rarity of the classes you want you don't have to base that rarity on the roll of stats. You can use point buy and if the player wants to play a paladin they can roll a d20 and if they roll a 20, they can play a paladin. The same can be done for other classes. Done.The chooseable options are the basics; if you want something special you have to roll for it and may or may not get it...this time. I do it this way for various elements of character creation, not just class. This allows rare-in-theory to be and remain rare-in-practice.
A lot of those ideas make more sense when you’re playing a high lethality game with a lot of PC turnover, AND you expect that the game will continue for quite a few real-life years.This tangentially raises another point: with point buy or standard array something I like to do becomes impossible: that being to gate certain classes etc. behind high rolls in order to make them less commonly seen in play and a little bit special if-when they do arise.
i don't know if it's the starting scores that really put MAD classes at a disadvantage so much as the progression that comes after that, i mean, it certainly doesn't help needing to invest in multiple high scores but while it's usually quite possible to get two decent scores and even something workable to stick in a third if needed especially if using array or point buy, but your tertiary scores do end up reflecting needing to invest elsewhere, but it's after that point, where two ASI only every four levels have to be assigned in different directions either slowing your progression to a crawl or going all in on one, and that's before you even start considering being able to take any feats!With point buy and background increases to ability scores, MAD classes are not a problem. My monk started with 16 wis/16 dex/14 con/10 str/10 char/8 int, which is great.
The problem I see here is you were forced to make a cookie, I mean a monk of average Strength, average Charisma, and below average Intelligence. You had very few options after ensuring that this monk had a 16* in both of its Primary Abilities. After that, you had about 15 different ways you could have gone. Which is still a respectable number, but when you chose to have a 14** in Constitution, your choices for the other three abilities were slim. They were either (8, 8, 12), (8, 9, 11), (8, 10, 10), or (9, 9, 10). You happened to choose the third option, which minimized the number of scores with a negative modifier to just one.With point buy and background increases to ability scores, MAD classes are not a problem. My monk started with 16 wis/16 dex/14 con/10 str/10 char/8 int, which is great.
Yeah, I was thinking about this today. The classes are each dependent upon one or more abilities, but they also have multiple scores that they are not dependent on. So, we make sure they stay low in order to make other scores higher. We "dump" them so to speak, because you can't really dump scores with the Dungeons and Dragons Point Buy method because they start at at 8. I would suggest (but perhaps I'm very wrong) that these "Independent" scores would usually/always be on the lower side or even "dumped".*So another monk will have the exact same ability scores as mine and yet be nothing at all like them.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.