Elemental Adaptation can ignore resistance, but not immunity. It also can't capitalize on vulnerability, and is exclusive to the one damage type selected when taking the feat (unless you take it multiple times, in which case... Well...). Not sure where you're getting the 2d10 force damage from warlock, unless you just mean eldritch blast... But the thing is, the 2d10 extra damage for burning a spell slot is applied automatically, without saving throw or attack roll, to every target within the scope of the spell. Which, all depending, can really add up. Sure, you can spend multiple turns to achieve the same effect for cheaper, but sometimes you really need things to die right now. Really though, it's more just to consider the amount of damage you'd normally be able to put out with a 1st-level slot by casting a 1st-level spell on its own turn, then compare that to simply applying 2d10 damage to another spell you're casting anyways on the same turn.
Also spell slots can be brought back via Arcane Recovery if you wanna use it for that, so it's not strictly 4 times a day, but I get ya.
And if your DM can be argued with, you can also kill the entire world by using a 2nd-level spell slot to modify Cone of Cold so that it's a mile-long cone... Which, by the time it hits the end, would have a width of slightly less than two miles. If you're into that sort of thing.
So, yes, several of the aspects can be either replicated or outdone by something else. However, it does all of these things within the scope of one class kit, which lends it a fair amount of versatility. Not only can you bypass damage resistances/immunities and exploit vulnerabilities, you can also change saving throws to something else (which can be a very big deal all depending on the situation, while only 'costing' one opportunity per short rest) to suit the target's weakness. And you get double proficiency on four skills, and you gain limited access to every spell list.
It's a lot of flexibility and a ridiculous amount of burst/artillery (even if it is expensive) all tied up with a neat little bow.