So, do some of y'all not recognize the irony of claiming "bards should be half casters because I think so" and "how dare they make warlocks half casters!!!"

"I want an arcane half caster because there isn't one and there are divine and primal half casters" and "I didn't mean MY CLASS!!!"

(I actually do see this potentially working for bards, though.)
OT....
I want to point something out that I didn't notice in this thread and haven't seen in other threads yet. Many abilities refer to spells from the arcane, divine, or primal spell list. That means, for example, the tome lock in the UA cannot use the
Book of Shadows cantrip to pick up the
Pact Familiar or
Pact Weapon cantrips. I noticed this in comments and it doesn't work because they are listed are not on those lists.
Hopefully that clarified it for anyone who might not have been clear.
Half caster is appropriate because of the amount of capability given within the invocations. The magic has been split between the spells and between invocations like before. Those limitations exist because of the additional capability in invocations.
The half caster is also there because players wanted more spell slots without needing short rests, and also because the devs restricted spell access for spells for which they were concerned a short rest recovery was potentially abusive. Opening the full spell list and still having short rest recovery doesn't remove that concern so feed back should include a critique of that concern. But this doesn't look random or arbitrary; it looks like a design inclusive of both of those concerns.
I gave it a chance and I'm ambivalent on the pact magic vs caster progression myself. I prefer the pact magic for a different recovery style but all in all it's the invocations that draw my attention to the class and the spell casting is secondary. There seems to be advantages in both and I don't mind the spell progression. That caster progression with a solid magical secondary mechanic like invocations works.
Moving some of the invocations into the class does ease how starved the class could be but requiring invocations to cover mystic arcanum reverses that. The only reason the the half caster works for me is because the mystic arcanum still provides access to high level spells like before, and that cost that was recovered by moving some invocations into the class was lost again.
It still seems to need about 11 invocations.
Level | Invocations |
1 | - |
2 | 2 |
3 | 3 |
4 | 3 |
5 | 4 |
6 | 4 |
7 | 5 |
8 | 5 |
9 | 6 |
10 | 6 |
11 | 7 |
12 | 7 |
13 | 8 |
14 | 8 |
15 | 9 |
16 | 9 |
17 | 10 |
18 | 10 |
19 | 11 |
20 | 11 |
Something like that. Another invocation early so there's one more most of the time and an additional one at very high levels. Allow for
mystic arcanum at 3rd level instead of 5th level with that additional invocation.