I think you're massively underrating his crossing. I'm not saying he sets the world on fire but he is an effective crosser.
Him and Januzaj have been our best crossers this season by some distance.
And I don't have any statistics to hand but IIRC Evra has an impressive assist/chance created record which is based primarily from his crosses. I remember the comparisons being all over SSN when we were heavily linked with Baines - that said for the 2012/13 season Evra and Baines both had the same amount of assists, Evra had the better cross completion rate (although he had significantly fewer crosses than Baines) and a better chance creation conversion. I'd have to look it up to be certain but I do remember basing those statistics around my reasoning for not wanting Baines at the cost we were looking to pay for him.
Again I never said he had the most effective cross on him, but to say it's terrible is wrong IMO.
Young and Valencia this year are examples of terrible crossing.
You don't get a consistent amount of assists (for a fullback) in the PL over 8 years if you're terrible at crossing.
He's not on the level of someone like Lahm, Alves, Marcelo etc but he's not terrible.