I don't agree that a warlock is all that simple. First off, it requires a far deeper understanding of the upscaling spells rules,
No it doesn't. Whether to upscale a spell is something that any primary caster needs to make just about every time they cast a spell. The warlock doesn't need to juggle options.
requires a lot of spell swapping every level to keep relevant,
This isn't play
at the table. Every 5e group I've had has levelled up between sessions when most people have time. Every 5e group I've had has also decided which spells the casters are going to cast at the table.
and you still have the "potion problem" of hoarding spell slots. I think they are rather complicated to play effectively, compared to a full caster who can survive just using the best blast spell of a given spell level.
If you're "just using the best blast spell of a given level" you're a wannabe warlock and probably underperforming the martials. Except warlocks you only worry about the best limited blast spell slot and Eldritch Blast. With a 7th level more normal caster when you want to blast you have to choose between the best 4th level blast spell, the best 3rd level blast spell, the best 2nd level blast spell, the best 1st level blast spell, and your best blast cantrip.
How, other than in the mind of someone who's spent literal decades playing wizards, is choosing between five separate levels of blast all of which do different things easier than just deciding "big limited use blast" or "at will zap"? And you still have the "potion problem"
Could this be improved with the warlock getting spells that scale better? Yes. But you are literally saying that it is easier to track five different types of blast, four of which have their own limited use pools, and which do different things than it is one limited use and one at will pool. This makes no sense.
I'd love for e.g. Hunger of Hadar to start as a first level spell with a 5ft radius that does d6 cold and d6 acid damage and scale up area and damage with the level it's cast at. Just as I'd love for the PHB to have not included a list of terrible invocations. But even with the clear lack of love and care given to the warlock (Hellish Rebuke not scaling I'm looking at you as another obvious case study) the warlock is still the simplest, easiest to play at the table,and arguably best feeling and most popular caster in the game.
IMHO, the allure of pact magic isn't simplicity or novelty, it's power.
Yes we get it. You do not like or click with the warlock. You click with it so little you think that six different options with five different limited use pools (as it is at level 10) is somehow simpler than two options with one limited use pool. You dislike it so much that you think having ten prepared spells that you re-choose when you level up is somehow more complicated than having fifteen prepared spells and a spell book of at least twenty three (and more if you are a cleric) that you re-choose every time you take a long rest.
We get you have literal decades of playing a wizard and it feels as if there is something missing when you are offered something simpler. What is missing is, to me and to many others,
makework that is not and should not be required to play a caster. And that actively slows things down at the table.
I am perfectly fine with trading the potential of six level 5 spells per day for a more guaranteed split of low to high slots. We're never going to agree on this.
We certainly aren't going to agree that the tedious and pointless makework of tracking low level slots makes the experience of playing a non-warlock more annoying and actively worse if you can not accept that the tedious and pointless makework of tracking low level slots is to many annoying and one of the points of Invocations is so you don't have to put up with that crap. We aren't going to agree that the warlock is simpler if you continue to maintain that it's simpler to pick from five options with four separate but overlapping limited resource pool than it is to only have one (or possibly two) limited resource pools to track. We aren't going to agree that it's simpler to only have one version of a spell you can cast at a time is more complex than having multiple different versions you can cast through upcasting.