I see what OP is saying, but I don't feel Rangers are hideously underpowered. Although what you get isn't that amazing, what you get comes at a very low ability point cost, which is why Ranger synergizes so nicely with the "utility character" concept of crafting, etc. If anything, giving Rangers the ability to actually allocate all of their ability points without hybridizing into something else (where "pure" Rangers are actually utility hybrids) might lead to such a pure Ranger being too strong, unless the current abilities were toned down. Furthermore, I actually appreciate the huge synergy between Crafting and Rangers, since they're very dependent on Crafting to have a perpetual supply of special arrows.
I'm far more likely to agree as far as Rogues are concerned. Unlike Rangers, where you can go utility and adjust for defensive weaknesses by playing "back row" and avoiding damage... Rogues need to be in the front lines to be effective, which means going utility or hybrid means cutting into defense and ending up with a squishy, often-dead Rogue. I mean, if you do the actual numbers, I would agree that maxing Sneaking with Guerilla ends up increasing your damage per AP, but so do ability points in One-Handed, and unlike One-Handed you pretty much have to max Sneaking in order to get the combo to work... so okay, Rogues can get up to 10 One-Handed points, but it's not worth it for them to do so until after they've already maxed out One-Handed in the first place. That's a huge commitment to melee damage without a lot of survivability to back it up.
What all of the above means is: Rogue ends up only being a good idea as a hybrid mixed in with Fighter (Str/Dex). Shield and dagger, Man-At-Arms skills, etc. Well, and I use a few of the lower-level Rogue skills (Fast Track, Walk in Shadow) on my daggerless Crafting Ranger. The idea of a pure Rogue, or of the Spellblade Dex/Int dagger hybrid, just doesn't work well currently; Cleric (Fighter/Caster hybrid) is miles ahead.
I think what the Rogue really needs is something to do with its off hand. Perhaps some form of dual-wielding; perhaps some form of Dexterity-based shield. Perhaps both; options are good. Or perhaps neither, and some other solution I haven't thought of yet. Whatever works. The point being, pure Rogue isn't a wise course of action at present.