Ooh, this is a fun game! Let's include spell slot levels and invocations in the comparison.I have to disagree with your disagreement then.
A day isn't long enough for enough hour-long breaks to have a warlock catch up with a wizard.
By level 10 a warlock has 2 spells per short rest as opposed to the wizard's 15 (plus his arcane recovery for another 5 spell levels). Assuming a four battles day, a level 10 wizard can drop 4 spells per battle without having to take a single short rest. The level 10 warlock will never be able to cast more than 2 even if there's a short rest after every battle. And if there's a situation when you can't short rest inbetween, you might be entirely without arcane spell slots in a battle even early in the day.
Wizard: 15 spells, plus arcane recovery in one short rest to get 5 levels of slots. We'll say that's one fifth-level slot, that would be the normal choice, so 16 spell slots totaling 41 levels. So in each of the four combats, the wizard can sling 4 spells with a total of 11 slot levels. If the combat lasts more than four rounds, or some of his spells aren't of any use in this fight, he'll fill out his other actions with cantrips.
Warlock: 2 spells, always cast in a 5th-level slot, for each combat. So he throws two spells with a total of 10 slot levels, then fills out the other combat actions with either cantrips or invocations. It's a bit tricky to compare invocations to spells; some of the warlock invocations are effectively daily uses of spells at a comparable level to the spells the warlock knows at that level, but those use one of his existing slots; those invocations add some flexibility (something to do with a warlock slot when your spells known don't match up with the situation very well) but not extra casting. Some let you cast utility-type spells of a lower level (or in a couple cases, the same level that's available when the invocation becomes available) at will. Others increase the power of your eldritch blast or weapon attacks. But you're only one total slot level behind the wizard in combat spells, so unless it's a pure utility invocation, you're more than caught up. The wizard doesn't have enough high-level slots to keep up; if he always burns his highest-level slots first, then by that fourth combat, his four spells are plinking with magic missiles in 1st-level spell slots, which is barely better than cantrip slinging.
Go to 11th level; the wizard picks up 1 6th-level slot, for 17 spell slots totalling 47 levels. The warlock now throws three fifth-level spells per combat, so 60 total levels over the course of a four-combat day. Plus he still has his invocations, and better hit points, armor, and weapons than the wizard. For combat magic, the warlock is way ahead. The sorcerer probably still beats him in that, but the warlock might still be ahead in total combat effectiveness. This is especially true when you consider that it's really your highest-level slots that are useful in level-appropriate combats. The wizard only has 3 5th-level slots per day (and one of those requires arcane recovery to gain, so he won't have more than 2 available in a given fight). The warlock can cast two fifth-level spells per fight, every fight (as long as there's a short rest between). He only knows two fifth-level spells, while the wizard could reasonably have five or more (depending on where he wants to keep his casting options), so the wizard could have a useful spell available in a situation where the warlock does not. The wizard only really catches up in overall power at the higher levels, when he starts getting 6th and higher level slots that the warlock just never has access to.
The big downside is exactly what I think the OP was concerned about--dealing with the odd outside-of-combat situations, or fighting foes with unusual resistances. The warlock just doesn't have the breadth of options the wizard has. Some of those come from the wizard's effectively unlimited spellbook & ritual casting ability, and you can catch up a bit there with the pact of the tome. But the wizard will always have more spells prepared than the warlock has spells known, and is selecting from a much more varied spell list. If you have a good idea what types of challenges you're likely to face in the campaign, you can try to pick spells and invocations that will be widely useful, but it'll be hit-and-miss. Guess wrong, and you suck forever ... Building a combat-master warlock is relatively easy, but that's clearly not what Eleclipse has in mind.
