I've seen a ranger (Savannah) competently tank all wings of HS numerous times. 2015 Rangers are great

I was just kidding. Nothing wrong with rangers.

This has been replied to before now but....
This isn't exactly true at least not in all cases.
If you've ever farmed the Dark Elf guards in Nektulos (good for plat) they can be a wide range of levels.
In and around the bridge in Nek the regular guards are level 15ish. The Corporals 20ish and the Sergeants around that too.
Dragoons will also spawn and they are around 35 if I remember correctly.
There is no cycle or predicting which will spawn in any spot that I know of

No you're right most guards can spawn with a wide lvl range.