I think it's pretty straightforward, honestly. Ranger as warrior is just a mix of sacred cow and misappropriation. The problem with the paladin is not one of categorization, but rather the fact that historically the cleric is already /also/ a warrior. I'm hoping we see that mitigated in D&D5 with domains affecting equipment proficiencies. A war cleric and a life paladin ought to have similar combat capability but very different class abilities..
I honestly think think that this summary is a good start to the discussion. To be honest, I am a big fan of DnD history and keeping traditions alive from the old days because it is what makes DnD what it is. But on the flip side, we need to look at how things have morphed with editions over they years. In the early days of DnD, before skills became prevalent you needed to have different classes to bring abilities to players.
With the advent of 3e (and beyond), skills have been taking a more prominent role in blurring class abilities (at least for experts). What I see is that we really have three groupings of classes:
1. Warriors
2. Experts
3. Casters
There are sub-types to each of those categories (of course). Now why am I stating the obvious?
What is a Ranger?
going old school: Warrior, with some stealth and tracking skills, and a few very minor Druid Spells
going new school: Warrior with combat tricks (TWF and Ranged) , bonus to tracking skills, medium-high skill points, more spells. Those pre-built in combat tricks to make up for losing class identity.
This kills me to say this, but in 5e should the ranger just disappear as a class? To be honest, it is basically a warrior with certain skills. The spells are very minor and could be moved to encounter/once per day type abilities.
Just make it a warrior and add traits/background to the character to give the ranger special powers (i.e. tracking, etc). If they want to pick up minor druid powers, then the same or a second trait/background to dip into that as a minor ability.
Is it really worth an entire class? No. I know backgrounds and traits are supposed to be optional, but honestly you can simplify the game by making them core requirements and solve a huge amount of issues. Plus, if we replace class abilities we help prevent power creep in the game.
Take a look at the cleric. It is primarily a channeler type (divine). To compensate for a lesser spells selection they pick up the ability to use armor and/or weapons.
Does the druid need a separate class? It may... but a druid is a cleric that has a background tree that replaces half a dozen class abilities (or less) and worships a nature deity (i.e. limited spell list by deity).
A barbarian as written is really separate enough as a class that it would stand alone.
Sorcerer and Warlock would be stand alone as they use separate mechanics.
Now to just change direction a little bit, I would like to see the following breakdowns for classes:
Martial - Primary combat based abilities
Expert - Primary skill based abilities
Channeling (Divine) - Power comes from a 3rd party (deity, spirits, demons).
Essence/Mana (Arcane) - Power drawn from the world around the caster
Ki/Mentalist (Psion) - Power drawn from within
(note - primal and other power sources from 4e can fit into one of the 3 categories above)
Those five definitions are a better description of classes than what they are proposing. They clearly indicate what they are best at. What secondary abilities they have beyond that are not relevant to be honest.
So if we look at things as a primary / secondary focus:
Monk - Martial (unarmed) / psion
Ranger - Martial / expert
Paladin - Martial / divine
Bard - Expert / arcane