But I'm sure you've noticed another flaw coming up with your blight example. That's that the Ranger doesn't have room to gain a 5th-level spell from the subclass feature at 17th level because it doesn't align with the subclass. The nearest subclass feature you can gain is from 15th level, before you can even cast a 5th-level spell. Thus, it seems underwhelming.
Try reading. I said 15th level.
And blight is a 4th level spell. Getting it at 15th level works just fine.
Better than monks who get the ability to cast a level 4 spell at level 17. Which is what the 4 elements monk gets. When the ranger gets their level 5 spells the monk can cast wall of fire. Their new power is one that the wizard has been able to do for ten levels
But let's not distract from the fact that your whole comparison is dishonest. Or at least incorrect. An elemonk can switch out spells as well as gain their new one every new discipline level. That can't be replicated on any chassis you try to put it on.
Sure ya can. Just have said spellcasting ranger get to pick from a small list of druid spells. Four spells, each of level one to four. Replace when you level up. Effortless.
If you can give the Ranger roughly 6 interchangeable spells that gives an effect unreplicable to other spells that the Ranger has access to, sure, I'd be fine with that. It would be weaker because the Ranger chassis doesn't support this model, but I'm looking for fun first anyways. And it sounds like fun.
It supports that model as well as the monk.
Subclass levels at 3, 7, 11 and 15 instead of 3, 6, 11 and 17. Both are effectively half casters.
It would be EXACTLY THE SAME to present a ranger subclass that gave it new spells,
Level 3 ranger. Gain druidcraft and pick one of faerie fire, entangle, purify food and drink or thunderwave
Level 7 ranger, pick one from the above or enhance ability, flaming sphere, hold person or moonbeam
Level 11 ranger, pick one from the above or from call lightning, dispel magic, meld into stone or sleet storm
Level 15 ranger, pick one from the above or blight, control water, hallucinatory terrain or wall of fire
Bam. Magic ranger done. Add 2-3 paragraphs of flavours and that's the subclass. Which I'm told will be balanced because it gives more options AND you claim it sound like fun. I expect a report of you playing one shortly. Feel free to write it up and add it on the GM's guild.
Anyways, off of your tangent, the monk (which is the topic of this thread), specifically the elemonk, is fine as-is.
How many 4 element monks have you played?
How many monks?