The fact that the Ranger is a partial caster and the warlock is, well, they get up to 9-level magic implies to me that the Blade relies more on spells like Hex, Armor of Aggy, Hellish Rebuke, etc for damage mid battle than the Ranger does. Further, the Ranger is designed to work with TWF, Archery, or sword-shield. The Blade is designed to work with just single handed finesse weapon - there's no heavy weapons, no shields, no archery, no armor variation. The only FS you could go with is Duelist.Look at it this way: the Ranger has both a fighting style and hunter's mark (which is equivalent to hex). He gets the benefit of both, while the Warlock only gets one.
Furthermore, the Ranger is only a partial caster; he doesn't have a lot of other concentration spells in his repertoire competing with Hunter's mark, so as he goes up in level he gets a lot more use out of it than a typical BladeLock will get to use Hex. Darkness or Hex? Greater Invisibility or Hex? The Ranger doesn't have these problems.
And I never said it was even footing, I was saying it was likely a design consideration. This and that are separate issues. I'm trying to parse not only the reasoning behind class design, but if its thematic or appropriate. The only reason I brought up Ranger was as proof that spells like Hex and Marks are designed as a necessary part of a class's power curve. Nothing more.