Nerfing mac's ground game with nothing to compensate would be pretty fatal for a character as... specialist, as he.
Just gonna engage in a friendly rant for a bit
No hard feelings, take it with a grain of salt.
Samus is a projectile 'specialist' and her moveset is pretty crummy and unsafe as a result of her apparently strong ranged game. A lot of attacks are built to not connect 100% of the time, like usmash and up B, leaving your opponents safe and with barely any damage. Jab doesn't connect at low to mid percents. Your bombs dont blow up on contact. Your attacks have huge lag. Your ftilt is slow, has low knockback, and does small damage. Your dtilt cannot kill. Etc Etc.
However, with all of these CQC drawbacks, she ALSO has huge endlag and drawbacks on her
projectiles. She isn't really rewarded with awesome projectiles due to having a reduced-effectiveness melee game.
Even though she is balanced with 'projectile master' in mind, she is in reality still quite lackluster in melee range when parttaking in regular CQC combat. Like many characters, she has to focus on her few moves that are reliable and safe, and has to rarely (if ever) use the rest of her moveset.
Megaman is a small arms specialist, yet his projectiles do small damage and cannot kill. He has 3 less moves than everyone else too, but you don't see him with superarmor or strong moves that 'make up for it'. But little mac as disproporionate amount of strong properties that make up for his lacking air game, more than any other character has whom has a lacking air or ground game.
Little mac gets to be the one with speed, superarmor, damage %, kill power, and range on his main toolset, something no other character really gets.
Many characters can choose to not fight in the air (or ground) because they are easily defeated if they stick to that area of play, but their ground (or air) game is not super powerful to compensate.
A lot of characters have specialties and focused designs yet don't have his treatment. A lot of characters don't actively use their ground game or air game due to them being worse options than the other, yet their good options aren't as powerful as Mac's.
Sure, Mac has a crappy airgame and doesn't use it, but many characters ignore large portions of their moveset in favour of strong and safe options. Jiggly's air game is not 'little mac' quality even though her ground game is barely used compared to her air game.It doesn't matter much that her ground game is better than Mac's air game, because it's not really being used all the same.
Plus Mac has a counter, quick fast fall, and a superarmor side B - these all help you get back to the ground quickly and safely. You're not as helpless in the air as little mac mains tend to make it out to be. Yeah, you have to ignore his aerial moveset, but a lot of characters have to ignore big bunches of their moveset, it's normal.
So yeah, being good AS little mac means avoiding being tossed offstage and getting back to the ground safely. On the ground, you have the upper hand against almost everyone, and as long as you focus on developing a skillset that keeps you on the ground, you'll perform at peak levels.
TL:DR: Other characters who similarly have to rely on their air or ground game, and ignore a large amount of their moveset in competitive play, don't have the strengths little mac does in his forte. He's fine.