I really enjoy crafting in this game. I barely crafted in FFXI because I could never really afford it, and I love that in FFXIV, you can start crafting with very little gil because of the leve system. However, the crafting UI is a good example of something in this game that "works," but still needs a lot of cleaning up.
I'm the other way around, as I enjoyed the way FFXI did crafting a bit more. Back in FFXI, crafting still took a lot of time and effort to level... But, if you had enough gil, you could shoot to cap in a craft in very little time. That was the exception though, in general, it still took quite a while, except much of that time spent was out in the field gathering mats, doing various things to make enough gil to pay for your crafts, making social connections to support you or scratch each others backs, etc. etc. etc. Once you had actually procured all your mats, it was only a few minutes of actually mashing synths.
Now, it's just raw hours of synthing... There's very little else involved in crafting... Maybe at times, you'll need to go gather mats, but even then, it's the same mat til near 50. I got to 40ish on cotton bolls. That's it. Just cotton bolls and the crystals needed to use them. Now it's flax til 50... Might be more varied in other crafts, but weaver is so boring in that respect. In ffxi, to cap leather, I needed a ton of different stuff, and getting out there to farm it, or earn gil to buy it took me all over the game, and I had fun with it.
But now?... You just sit and synth for hours upon hours... Gil just drops in your lap, so you can just pile up on mats and go back to the synth grind. Sure it seems great early on, but later, it really wears on you, which is why I've made about 2 levels in weaving since december. I guess it's a plus that people can't just shoot to cap anymore, but honestly I'd prefer dealing with that and have a versatile and fun crafting experience, over it being what it is now.
Either way, my best advice is to either make crafting parties with your friends, or do something else while mashing A with a gamepad. Then crafting can still be fun. But without either of those things, I probably wouldn't have made it past 30 weaver, and I loved crafting in FFXI. At least they made harder synths give more sp now, so it goes twice as fast at least.
As far as tweaks to the actual UI... Higher framerates for actions, getting rid of all the extra pop up windows, and a dropdown menu for tool selection that, like was said, stays selected indefinitely until you change it, would all be welcome. And rapid synth needs a buff so it's viable during SP synths.
But I don't think they should eliminate the offhand tool. They do serve a pretty good purpose. Sure, with trivial things like cotton yarn, you might think it'd never be worth going for a few extra when you can have HQ ones instead... But for example, when we got our first Dodore wing +3... It was a tough call whether we wanted offhand, for a chance at HQ doublet mats, or higher yield, for an extra doublet. We ended up going for higher yield since the highest offhand tool has crummy stats compared to the highest mainhand tool, but still, nice to have that choice. I'm sure future items will also be like that too, where both tools offer very tempting results.