I can't remember when they gave shortbows back to the rogue - but I think it was pretty early on. 4e rogues could be archers (I've played a few) and this didn't miraculously break the ranger. And this is little different to the rogue in 5e where Sneak Attack says that "The attack must use a finesse or a ranged weapon." (I think the only non-light blade finesse weapon in 5e is the whip). And then there were other builds for rogues that could use saps and maces.
And yes they did add dual weapons to the fighter less than six months in, complete with abilities that synergised with it. 4e fighters were mostly exclusive melee (and good at it). But the niche protection you are talking about wasn't really a thing.
Not so. That's just how it was at launch. I remember some two handed options as well.
No you wouldn't. You yourself mentioned that fighters moved into the TWF niche - as for that matter did barbarians. Meanwhile Rogues were allowed bows. As were Seekers, as for that matter were clerics though I never saw a Cleric of Sehanine in play. And there was even one fighter subclass (the Slayer) that could use bows.
None of this in any way stopped the Ranger. Because actual care was put into making the ranger good at what they did - and setting the benchmark using them.
In other words pretty close to the way 5e does it by having sneak attack working only with finesse or ranged weapons and the rogue not having longbow proficiency so needing to invest resources to use something bigger than a shortbow.
Except that as 4e proved that was not needed. It was just something done at launch either because the two weapon fighter wasn't ready or they couldn't fit it in the PHB (or both). But a lot more care was taken in 4e making the ranger's TWF (a) good and (b) distinct from the fighter's which was again distinct from the barbarian's than 5e seems to want to take.