I'll grant you that a Half-caster Ranger is going to have more spell slots, higher spell slots and a faster progression than a Third caster Ranger subclass. But the difference between the two isn't big enough to really make the former better than the latter
Actually it does.
The The way you get spell slots in D&D you will get a whole lot more spell slot as a half caster compared to a third caster which allows you to use those slots a lot more.
It's an actual huge difference.
As for spells tailored to the class, they would have to be spells that only Rangers can have. However, magic that has been tailored to only one class doesn't make a Half-caster Ranger any better a Third caster Ranger subclass either. It's what you chose for your Ranger character that makes it better for you
No they wouldn't because almost every designer does not create spells specifically for subclasses.
It's a matter of focus by making it so class you put less focus on it and have less likely a chance of it being created.
It's just like how people say that the Ranger is just a fighter druid They won't create a spell for the Ranger they will just create Druid spells.
There aren't any Rangers spells in the original class book for A5E.
It's the same reason why there's no ranger maneuvers in WOTC 5e.
The farther back in the bullet points the trope is pushed into, the less likely the designers will design specifically for it.
Again, you can use either version of the WotC ranger (all three including Tasha's) in an A5e game if the DM agrees. That way you can have your half-caster version.
That's the point.
They are two different classes.
You cannot combine the two ideas into one class.
However the community constantly fights to only have
one Ranger class slot.
So you either get a Martial Ranger with bad magic or a overtly Magic ranger with weaker Martail ability.
Designing both in one chassis requires having a deep thought about the core flavor of the class and how you would balance those mechanics while truly respecting both aspects of the community at the same time.