No apologies necessary. Go right ahead.
I will note though, that only discussing the designers intent does not actually solve anyone's problems. The book is printed. It isn't changing. If you don't like the ubiquitous of magic in 5E... well, too bad. There's nothing you can do about it at this point.
So I was actually just... you know... moving forward. Providing a solution. But if none of you WANT a solution and would rather just continue to wallow in your own annoyance... hey, feel free.
Honestly I still feel like this is less of a
game issue and more of a
setting issue. Lets say we make "NewGame", NewGame has 10 classes, 9 are casters of some variety, 1 is a non-caster. Yet, New Game is set in Worldland, and in Worldland there are a wide variety of different ways to use magic....however to use magic is difficult, dangerous and in some places, illegal, so casters are actually very rare in the setting. Most people in Worldland who aren't mundane PeopleFolk(TM) are variations of the one martial class in NewGame. A dozen varieties of soldier, rogues, rangers, and so forth.
D&D certainly has progressively allowed more classes to use magic, no argument there. But assuming you had the option to multiclass, all NewD&D has given us is pre-baked multi-classes classes. What is an Eldritch Knight but a Fighter/Wizard? An Arcane Trickster but a Rogue/Wizard? A Way of Four Elements Monk but a Monk/Sorcerer?
We could strip out these options in NewGame, but if we're not going to prevent players from multiclassing, it's natural that the rule-bending nature of magic is going to attract people after "hit things with a stick" becomes worn out. But what has NewGame really accomplished in removing these default options, or even outright banning multiclassing? At the end of the day, it is more important
where you are playing the game than what is available to play.
Playing a Water Mage in the Sahara might be difficult. Playing A Sand Sorcerer on the other hand may not. So if your setting is the Sahara, why worry about the fact that someone
could play a Water Mage? The default assumption of the setting is that water is rare. Even though both Sand Sorcerers and Water Mages have equal number of classes in the rulebook (that is to say, one), their prevalence in the setting is unequal.
So if Worldland says that magic-users are rare, even if you have a whole party of magic users (4-6) that's 4-6 people in the WHOLE WORLD. 4-6 out of potentially millions of people. Just because the game story focuses on them doesn't make them any more or less prevalent in the world. You're talking about a .00004% difference in the magical population of a setting. Statistically, it's insignificant!
So if magic use is "too prevalent" for your (hypothetical your) tastes, just say it's rare in the world. Poof, now it is! I'm currently running a super-low magic setting, where there are probably oh, 5000/1 magic users. The whole PC party uses magic though! That just means there are at least 20000 (I have 4 players) people in the world...which there are way more than, so it's not a problem, not even close.
To sum up: The Game(TM) is just a set of rules. Without a setting to determine prevalence the fact that all 10 classes can use magic in some way is meaningless.