Nice to hear. I think a lot of people are still stuck in "I'm no For Glory scrub!" mode and are underrating him
Is Tornado Uppercut good? Don't have a lot of experience with his customs
LM customs:
Flaming Straight Lunge - Faster charging, multi-hit, less damage, dubious recovery utility. No armor though IIRC.
Stunning Straight Lunge - Slower, hits people behind you, pointless stun element. Seems pointless.
Note that both neutral B customs give earlier super armor on KO Punch.
Grounding Blow - High, short arc to jump. Spikes aerial opponents, buries grounded opponents. Links to Rising Uppercut. Laggy.
Guard Breaker - Super slow, super laggy, short jump. Covered in super armor starting on like frame 9. Does 18%, unblockable.
Tornado Uppercut - Trivial height gain, pitiful damage/threat, terrible.
Rising Smash - Absurdly slow, but absurdly strong. Worse recovery height unless combined with double jump. Cannot combo out of bury.
Compact Counter - Faster ending, low (fixed) knockback counter.
Dash Counter - Weaker counter that sends Mac forward. A bit too slow to be a practical projectile counter, but good for recovery.
Little Mac has no slam dunk customs, but his radically different (and all useful) side-b options are very important on a matchup-by-matchup basis.
I know that it's easy to forget this when discussing the competitive environment, but we have to assume that Little Mac was designed to be usable at least to some degree on not just the stages that are "viable" according to community standards but also every stage in Smash. This means walk-offs (where I assume Little Mac is a tiny god) and moving stages with hazards (where Little Mac is super boned). In a way, this reinforces your argument, but if we're talking about a character designed to be polarizing, I think he was actually designed to be polarizing with those more extreme stages in mind, and not so much the ones that are just used in tournaments. In those stages, he'll be pretty advantaged/disadvantaged overall but I wonder if this isn't exaggerating.
Also keep in mind FFA-Stock, FFA-Time, 2v2, and 4v4 environments--all of which LM does significantly better in than 1v1. (It's harder for EVERYONE to avoid him, and their are higher costs for doing so.)
For an even more extreme case, look at Zelda.