As for 1.8.4 update, XP scale has improved, but it does not prevent the good old "spam 0.3 sec gear hendcraft" abuse.
Let me elaborate:
You use square root, so the longer recipe is taking to craft, the less bonus XP you get per craft, which again makes handcrafting of longer crafted items redundant, as you have the best option from the start.
So for now, it seems like 1 sec of craft is worth of 10 XP points at base.
0.5 sec gear craft yields to 5 XP points.
10 sec accumulator craft should yield 100 xp to be at least worth as 20 gears, that can be crafted at the same time...
But it gives 22. So there is no point of crafting accumulator or any other long crafted item, cuz I can get 5 times more xp just by gear spam.

So my idea is that:
Take the base crafting XP of 10 per second, make each craft to give at least that amount * crafting time. Not less, cuz otherwise it is obsolete.
Than add some bonus using formula (linear or inverse square root), so the longer item crafts, the more xp it would yield.
The expected is to be:
0.5 sec gear craft yields to 5 XP points.
10 sec accumulator craft should yield 100 XP PLUS some bonus. That way the best thing to craft is the longer one, like Space Platform hub (60 sec, not very costly), robot frame (20 sec, cheap) etc.

Perhaps there should also be item cost involvement but one step at a time.
Yeah, I probably should not overanalize it, cuz anyway handcrafting should be redundant later, but still.

I see, I will update this tonight, going to take a quick pass as I want to play a bit, but fixing the XP curve is high on my immediate list.

Updated for 1.8.6, after 500 crafts they'll be no exp from gear wheels, allows for some early game progression without making it last to late game. This applies too all recipes that take under a second.

Will need more balancing in the future, but for now the gear wheel farm shouldn't be a thing. I am still fine with longer crafts giving good exp, but soon it will probably be subject to the same diminishing returns - this is a broader points availability issue and will be part of the balancing run later on.

The play it your own way will always exists, if someone wants 100 points per level, I am not going to stop them, but the default will at some point be one and skill cost adjusts accordingly.

Great!
Have not thought myself about hard limitin crafts, good idea.

It was a logical step, you can't change the 0.5 craft time and some skills actually reduce it. So capping that item and others made sense.

I'll need to start a fresh game to see how that works, but we both know this mod is far from balanced at the moment :)

But so long as it's fun!

I've started a playthrough with bunch of mods, and also using yours, so maybe that will tell something or give birth to new ideas.
But I will not use some features at least untill rework. In particular:
XP abuse (for more fair and real gameplay)
Alt recipes (I told you why)
Knowlege tab (useless)
Production tab (too strong even by itself and I also have mods like "Extended Vanilla: refining", so combined productivity will be absolutely insane)
Capstones (not cuz it's bad, I just don't need or don't want neither of present two)

All that can be tuned, my main focus is currently skill points, how they unlock, assignment, linked/ pre req abilities etc. When that working on a base level more attention can be paid to fine turning some of the skills.

Keep the suggestions coming bud.

Knowlege tab (useless)

I had to take time and reflect on this, and get around to looking at it.

There is a random +8 inserter stack bonus and alot of research speed. The bonus needs to move, and there will be an element of research Speed in the tree.

I like the idea of a Knowledge tab, I think it may sit better with increasing productivity (when making) each of the science packs, .Potentially grouped:

Early Science: (Red/Green/Blue)
Late science knowledge (mil/yellow/purple)} Mil is a bit of our outlier.
Space Science: The rest.

Still not convinced about the entire tree as either way it comes down to impacting the core gameplay loop significantly.