Your hypothesis is a bit off

There is no iLvL 70-90 crafter/gatherer gear that can be converted (As I know of, maybe I am wrong)

They never said conversion rate for the lvl 45-49 gear is changed and won't drop tier IV.

And the spiritbonding is now faster if we are doing content in the correct level bracket in regards the level of the gear.

For the melds I look often at this post.
Lots of solutions not all tier IV dependent

http://forum.square-enix.com/ffxiv/t...ted-for-2.3%29