I think that if we get our 3rd invocation at level 3 and not level five, then an extra one every two level there after it might be ok. Also I would add the ability for level 2 mystic arcana at level 3.
This way we get an extra invocation at level 3 an can use it to get our first 2nd level spell. At fifth level we gain second level spells and can swap out our mystic arcana for a 3 rd level spell.
Since most warlocks would have spent an invocation at level 3 or 5 improving their pact ability but those have now been rolled into the basis pact cantrip it frees up an invocation for picking up a utility invocation you like.
At 7th you will want to spend your new invocation on a 4th level mystic arcana.
By ninth level we are in a much better place, we have our 3rd level spells with frees up an invocation to spend on a 5th level spell and still lets us spend our new invocation we just got on one of the 9th level pact specific invocation
11th level we have to spend our invocation if we want a 6th level spot. This is when we start to feel a bit of the crunch with not having enough invocations even by giving us an extra 1 earlier on.
At 13th we now have fourth level spells but only one but we can swap out our 4th level mystic arcana for a 7th level so we still have our new invocation to spend on what ever we want.
I would still suggest an 11th invocation at 19th level even if it is late in the game just for more versatility.
With a small bump to the invocations you get and the addition of 2nd lvl mystic arcana at 3rd level you have 4/1 spells (with 2 free invocations), at 5th 4/3/1 (with 3 free invocations), 7th 4/4/1/1 (with 3 free invocations), 9th 4/3/3/1/1 (with 4 free invocations).
Compared to a 9th level 2014 warlock you have the same number of free invocations (assuming you took the pact specific one). The 2014 would have gotten 4 maybe 6 5th level spell slots in a day compared to 4/3/3/1/1 so 2 or 3 times as many
spells but of a variety of levels. If we broke those spells down into spell points the 2014 warlock has 28-42 spell points worth of spells while the 2024 has 45 points worth of spells.
Even with out my preferred change of adding more invocations an 2nd lvl mystic arcana you are only 1 invocation short from what the 2014 has for more spell power spread across more all be it weaker spells.
Over all the biggest problem is in levels 3 and 4 without your 2nd level spells and no way to gain those you fall behind in the power curve.
