Fiddlesticks, the ranger has to be self-reliant. Any ability that he lacks that keeps him from being self reliant he should be allowed to pick up. A ranger that has to depend on a party to survive isn't a ranger... he is a guide.
D&D is a game about parties of adventurers. Not one ranger OR a party of everybody else.
But there is some truth in the idea that the Ranger is more self-reliant compared to others. Only in the wilderness tho. There is no reason why a Ranger should be completely self reliant in a dungeon, or in a city. And in the wilderness you certainly don't normally need social skills for instance, so at least a Ranger shouldn't by default be good at them, he should be able to pick them up at best just like everybody else is, but others can definitely be better.
A rogue needs the skills to cheat, lie, and steal. That's why he has always been good with scrolls and other pilfered magical items. That's why he has never been particularly good at skills involving honest work, fighting, and casting spells himself. Any skill that doesn't help him steal is useless to the rogue, and therefore he doesn't fit the jack-of-all trades mantle either.
Rogue is not thief (at least hasn't be so since 3ed).
Rogue is someone who compensates for lack of competence with a mix of ingeniousness, sleight of hand, improvisation... anything that works.
You are right that he's never been particularly good at working, fighting, spellcasting. He uses "workarounds" for those: tricks, fighting dirty, hacking devices and (in some editions) even magic items. The fact that he is NOT good but he CAN make it, is practically
the definition of "jack-of-all-trades, master of none", although it's not true that the Rogue is master of none... traps and stealth at least are definitely something he excels at.
If you're trying to say that there should really be a jack-of-all-trades that is really good at everything (to the point that he can play alone like you seemed to mention about the Ranger), that's not really acceptable in a
role-play game, IMHO.
The bard wanders between inns and the courts of nobles. So he doesn't really need to be self-sufficient in the wild. He needs to learn basic defense, but he doesn't need to fight well enough to defend himself from all comers because he always travels with others. There is no reason as well that song magic has to be less powerful than other forms of magic, but it is arbitrarily reduced in power because we are loading him up with rogue and fighter abilities that he doesn't need for his basic concept to work.
That's the thing, the more we make the bard a jack of all trades, the less he is good at the things we actually want him to do. Namely, being really good at social skills and songs.
I also want the Bard to have something he excels at compared to anyone else, social skills and songs are definitely the best choice.
But in retrospective, the Bard IIRC started off in earlier editions as part druid - part warrior, then got a more travelling/wandering flavor, and only later was commonly associated with courts.
