Now listen. I don't think Meta Knight is bad or low tier, but his damage output and kill power are abysmal. I swear, he does like 80% less damage than the rest of the cast and it's annoying. Not to mention, his Smash attacks are mostly unsafe, and all his specials have so much lag, that they're almost never useful besides recovery and edgeguarding.
I agree, his attacks have extremely low attack power and his specials leave him very vulnerable (besides his teleport if you don't attack). However, the main strategy with Meta Knight is to use your neutrals/grabs (which are extremely fast) to try to knock your opponent into the air or off the edge and then just edge guard them.
Meta Knight is one of the best edge guarders in this game, and you can absolutely destroy opponents when used correctly. Because his up/down aerials have weak knock-back, it is possible to juggle your opponents very high up and finish them off with Shuttle Loop, or you can juggle them off the edge, use your up/down/neutral aerials, and then use Mach Tornado to KO them (it works even when your opponent has low percentage). This strategy requires a lot of precision and timing, so you may need practice for this.
The only characters that Meta Knight is weak to are zoning characters (especially Mega Man), and trying to edge guard characters with good recovery (like Joker) can be difficult sometimes.