this small sphere of doom

you seem to be forgetting a metaknight counter, but its understandable since like 10 people play him total (me being one)
Dk wrecks metaknight, hes got more priority, more range, and waaayyy more power. one top of this, ftilt hits through mach tornado.

sure, metaknight is faster, and can combo, but a dk player is used to that (anyone who plays fatties gets used to being combo'd by everyone), and after its over, i have like 40% more damage, but it doesnt matter because dk lives up to 200, on top of this, dk has 5-6 moves that will kill you at 70%,

i've made 4 metaknight players switch to d3, 3 were scrubs, 1 was edge

DK doesn't have more range lol. The only exception to this is his B-air which is beastly as hell. Also, all of DK's kill moves are relatively hard to hit with besides the D-smash.

metaknight is definitely the best character lol

perfect hitboxes, decent enough kill power, up-b, recovery is flawless, perfect edgeguarding, small, multiple jumps, glide, sword of destruction aka perfect hitbox

I think they get the point BF, but like you said, all of ten people play DK, so he is not worried about so much.

Let me compare Meta-Knight to another character most newbies like to pick up at once: Ike.

Now, new people like to pick up these two characters when they first start for one reason: They're easy to use. Ike for his power ( An uncharged Fsmash kills at 40%, Charged at 15-20%), MK for his moves. The newbie smash players using these two will spam their priority moves.

That being said, once they try them, they realize that Ike is harder to use than they thought, but this topic isn't about Ike, is it? No. MK on the other hand, Newbies will stick as for longer that Ike, due to easier priority. Once they go up against even more skilled players, they realize that MK has his fair share of easily exploitable weaknesses. Most of his kill moves take a high percentage, and are hard to connect. The afterlag on MT and Drill Rush can set MK up for a semi-charged Fsmash from a few characters, possible killing MK.
 
Also said earlier, Vertical kills are how MK is KO'ed more, Horizontal Kills are almost impossible unless at high percents. That said, if MT or DR are used in the air, the after lag MK has during the fall can set him up for a powerful Usmash from say.... Fox.

Now, I would normally continue, but I'm tired and need to sleep. MK is not broken, but he is certainly one of the stronger characters in the game.