First off, I think the title is not the real question. Warlocks aren't just eldritch blasts and have other features which make them useful (i.e. ability to use/craft virtually almost any magic item). So it should be better phrased as "do reserve feats make eldritch blasts redundant?"
Here are some advantages of eldritch blasts over reserve feats:
1) Range. It's the difference between a monster being able to reach you in a charge or not.
2) Energy type. 1 Reserve feat gives you access to one energy type. Eldritch blast doesn't really have an energy type, and thanks to invocations, it can be changed (if a monster has a vulnerability for example). With reserve feats, you might end up facing a monster that has resistance or immunity to your stuck element.
3) Shape. Again, thanks to invocations, you have a variety of shapes available to you, or at the very least a ray. Reserve feats that deal damage usually come in a fixed shape, and you have to worry about hitting allies if they're not in optimum positions.
4) Damage output. Eldritch blasts in general has a higher damage output. No need to compute what spell slot to "save" and various factors can increase the damage dealt by your eldritch blasts (metamagic, magic items, etc.)
Also, here are the limitations of reserve feats:
1) It's costing you a feat!
2) You have to "save" a spell slot in order to use it. Although sorcerers in this case have it easier than wizards, but they also get less bang for it (because wizards have less slots to utilize than sorcerers).
3) Limited type of damage and shape. Granted, ability to dole out damage "for free" is better than none, but it's nowhere as flexible as an eldritch blast.