Steelix has all the makings of being a great defender. The downside is it's weak to a lot of common counters. Don't even consider it for offense.
Scizor is a good niche attacker - it doesn't have a lot of roles but it does them pretty well. Not that great on defense due to double fire weakness.
If you need it for a Pokedex filler go ahead. Unless you come across a Scyther nest you'll likely get another Metal Coat through 7 day spin streaks or from opening gifts before getting the candy to evolve one.