You know, you came off really harsh, but you changed my mind.... Slightly.
It was an issue I didn't realize existed until I had it pointed out to me, by yourself - There is a level of satisfaction you get from tiering weapon unlocks, so you don't just wind up smithing the same afk piece of armour from 1-99. Thus naturally giving you that excitement behind the next unlock.
I certainly agree that unlocks at every level is desirable. (It's why Mining and Smithing have systemic upgrades inbetween the tiers.) In the case of Crafting, since it's a catch-all artisan skill, there's a variety of things to craft other than equipment (jewelery, pottery, etc) to help occupy the level gaps. If there were skills exclusively for Leatherworking and Tailoring, I'd agree big gaps between equipment tier unlocks would be a significant concern.