Klinklang isn't too bad. It's just a little...underpowered. Steel-types aren't even it's biggest problem in OU. It can run Hidden Power Fire & deal with Ferrothorn, Scizor, Skarmory, & Forretress. Heatran & Excadrill force it out of course. (Metagross isn't really OU anymore, guys...no idea why now that Chomp's gone...) Exca would force it out even if Klinklang had Earthquake.
The problem with Klinklang is that it doesn't have enough power to muscle through a team. A lot of Pokemon run just a little too much bulk to be KO'd by Gear Grind. Let's face it, Klinklang can't take more than 2 hits from anything especially if we have to decrease a Defensive stat to use Hidden Power with decent power. And then you have the Pokemon that resist Gear Grind. Return doesn't OHKO much at all at +1. The damage for Adamant +1 Return vs 0/0 Starmie is 86.6% - 102.3% which says how much this Pokemon NEEDS Stealth Rock to pull off any kind of sweep. Kinda annoying really. You not only have to get SR up & keep it up, but you have to basically clear a path for Klinklang, getting all bulky Water, Fire, & Electric-types out as well as Excadrill, for it too sweep. That's a really steep order for any team.
Could you use Klinklang in OU? Yes. Is it a good idea? Hell no. Klinklang wouldn't be good even with Earthquake. Better, but not good. If it had Earthquake AND Wild Charge, we might have a Pokemon here. Oh well.