I can live with the complexity, IF, points can be reused to cast a spell and oppositely, a slot can be reused to modify a spell.
Here is comparable situation regarding the multiclass Warlock/Sorcerer. The citation comes from stackexchange about 6 years ago. I am unsure whether players tend to like or dislike this multiclass situation.
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Question
Multiclass Warlock/Sorcerer: How do spell slots recover?
If you multiclass a Warlock and a Sorcerer, then you have a character with both the Spellcasting and Pact Magic features.
PHB Page 101, Sorcerer, Spellcasting, Spell Slots:
You regain all expended spell slots when you finish a long rest.
PHB Page 107, Warlock, Pact Magic, Spell Slots:
You regain all expended spell slots when you finish a short or long rest.
PHB Page 165, Customization Options, Multiclassing, Class Features:
Pact Magic. If you have both the Spellcasting class feature and the Pact Magic class feature from the warlock class, you can use the spell slots you gain from the Pact Magic feature to cast spells you know or have prepared from classes with the Spellcasting class feature, and you can use the spell slots you gain from the Spellcasting class feature to cast warlock spells you know.
Do the spell slots keep their previous method of recovery (sorcerer slots long rest, warlock slots any rest), or do they all act consistently as I am led to believe from the language of the multiclass section? Do they all recover only from long rests as per the sorcerer feature, or can they all be recovered with a short rest because the warlock feature says so?
Your spell slots recover based on the class feature that allows your spellcasting.
Answer
The language in the multiclassing section only mentions how you cast spells, not how you recover them. Note that recovery isn't mentioned at all in that paragraph. The spell slots are interchangeable when you're casting, but they recover based on their own mechanics. Unlike spell slots from multiple classes with Spellcasting, they don't merge into one pool; they remain separate except when you're actually casting out of them.
As a Warlock/Sorcerer, you have both the Pact Magic feature and the Spellcasting feature, which recover spell slots separately. Pact Magic slots recover on any rest, and Spellcasting slots recover on a long rest.
Other Answer
The key point is that Warlocks don't have Spellcasting at all. They have Pact Magic. Despite sharing a lot of similar terminology - spells, spell levels, etc - they are different abilities with different rules. The multi-classing rules present a bridge between them, but they're still different abilities.
Question
I think this might be related: Is it possible to “charge up” a sorcerer/warlock by taking multiple short rests?
Answer
I would like to point something out on page 164 of PHB, in regards to this question:
Spell Slots. You determine your available spell slots by adding together all your levels in the bard, cleric, druid, sorcerer, and wizard classes, half your levels in the paladin and ranger classes, and a third of your fighter or rogue levels if you have the [...] features.
Note that Warlock is not listed. You do not add Warlock spell slots to other spellcasting classes to achieve a total as per the chart on page 165 PHB. You keep them separate. Thus specifically your Warlock slots are the only short rest recharged slots. Maybe that'll ease some confusion, and happy gaming.
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As such, it seems that the Psion will be in the same multiclassing situation that the Warlock is in.
I am unsure if this is ok or problematic.
Note spells of slots 6 to 9 dont use spell points, so it seems both the Sorcerer and Warlock ... and Wizard and Psion ... could use each others slots for these levels, as is normal for the Spellcasting feature.
