Metal Blade isn't necessarily worse, just different, and it has its own tech that sets it apart from our own gyro. Throwing it into the ground and picking it up again makes it do more damage on the rethrow, for example, and of course Megaman's glide toss is much longer than any other item character can really boast.
And really, that's the same for a lot of his projectiles. Lemons are weak but fast, making them easy to outprioritize but difficult to punish otherwise. Crash Bomb forces opponents to either take the damage (bad) or shield the multihit (what Megaman wants you to do). Leaf Shield....I honestly have no clue, fairly certain that one actually IS bad.
Going off of your quick Brawl one-off reference, comparing his stuff to ours is like comparing Brawl MK to Ice Climbers. They're both amazing picks (and in fact it can be argued that Ice Climbers are actually BETTER, crazy as it sounds), but their strengths and weaknesses are drastically different. If you try to use Megaman's projectiles the same way we use ours, it won't work, because they're not designed to BE used like our projectiles.
(Another note on your Brawl reference, Meta Knight actually DOES take skill to play in that game- a big part of why he's so good is because he has a myriad of tech to choose from. Hence why I'd rather fight a good MK than, say, a campy Brawlimar that can get results without much understanding of the character.)