If you're good enough, you're old enough is the common saying
If you're good enough, you're young enough.
We know that we're weak at times in the 2nd row.
It's not about being an enforcer going around looking to punch someone, but about someone who doesn't take a step backwards, who makes a yard or 2 in contact, who isn't easily driven off the ball at the breakdown.
Mobility, handling, and slowing the ball down are all very important traits, but when you're a team who are often beaten up by opposition packs, a powerful lock is invaluable.
Joe Launchbury doesn't look like he should be that man, and maybe 'powerful' isn't the first word used to describe his play, but he's way ahead of the rest of our 2nd row options.
Someone like Scott Fardy wouldn't need to play every game. He could play when Joe is away with England, he could be a bench option when Joe is around, or allow Joe to have a rest, while ensuring that we can still compete at the power game.
I just don't see the downside here providing he's not on a million pound per year, and providing he's still able to put in a solid 60+ minutes every time it's required.