But those things are what make the ranger, well a ranger. Take those away and you have a fighter with certain skills. Rangers are a specialized type of class so the design of the class does require specialized things. Something stops being special when it works in all scenarios. I think we are also forgetting that DM's run the games and don't run these things blind. When I create a game, I find out what everyone is playing and I tailor the game to any of the specialized classes. That is why Hunter's Quarry from 4th edition was so awful and bland. They took the specialness out of it and made it seem like it was tacked on just so the ranger could do top damage to every creature.
In most specialized classes, the scenario that governs their specialty changes with the tactical situation
from round to round. Some rounds the rogue can make a sneak attack, some rounds he can't. Some rounds it's important for the barbarian to absorb a ton of damage, some rounds it isn't. Some rounds the enemies are clustered up for a nice fireball from the wizard, some rounds they aren't. Old-school favored enemy, in contrast, changes in effectiveness
from session to session. Some nights the party is fighting giants and the ranger is a rock star, some nights they aren't and she might as well not show up. This difference in spotlight time duration is of huge importance. If the player feels like she only has to wait a couple of rounds to be awesome, that's fine. But if she feels like she might as well not have shown up, that's demoralizing. It may not be demoralizing to you or your players necessarily, but it's demoralizing to enough players to make mechanics like this of serious concern. And for the sake of illustration, I'll mention that favored enemy is not the only old-school mechanic that does this. Another major culprit is the differing power curve for warriors and spellcasters, where the spellcasters can feel like they're useless for months, then the table turns and the warriors feel like they're useless for months after that. The goal in game design should be that the spotlight falls on each player character pretty reliably several times a
session, not several times a
campaign.
And no, the DM writing his adventures with players in mind is not a sufficient patch for the problem. Your own logic betrays you here: if the DM makes the campaign
entirely about fighting giants, then the ranger's ability works in all scenarios and doesn't feel special, but if he makes the campaign alternate between fighting giants and other things, then we're back in "why did I show up tonight?" territory. Plus, speaking as a DM, I like to have a little bit of leeway in how I design my adventures. If players want to play a campaign where their primary activity is bold and heroic giant slaying, they are capable of communicating that to me in the same way they'd tell me about any other campaign preference. They don't have to take a character option that mechanically punishes them whenever they're not fighting giants.