This is all true, obviously, and discussing football will always be a matter of opinion.
I just felt that Herrera would give us a better first XI option in CM, while Fellaini wouldn't to such a degree. As I said it isn't the typical "Spanish" qualities that makes me feel he'd be a good fit, but his tenacity, his work-rate and his tackling ability combined with the mobility and passing which Fellaini quite simply doesn't offer.
And it's unfair to hold Herrera's lack of caps against him - Fellaini wouldn't be capped if he was Spanish, either.
But all of us obviously won't agree on this - I sincerely hope he succeeds, but would have preferred someone else as our only CM signing. In fact Fellaini would be quite far down the list for me, but there you go.