This bears repeating again. Level 8 might not seem like a high level now, but in AD&D it was. This context is very important. Yeah, rangers eventually got spells. But most of the actual time spent gaming with them, they didn't have it. Just like thieves casting spells off of scrolls. Sure, they could eventually do it, but it was hardly what people considered a big chunk of their identity. Especially since AD&D had a much higher lethality than modern editions, and many of your PCs did die before they got to high level. I don't think as many 3e PCs died before making it to level 4. This isn't some brief offshoot of the class we're talking about either, but how it was built for the majority of it's entire lifecycle in D&D.
You shouldn't assume that the way you played was the way everyone else played. Yes, characters in AD&D died a lot at lower levels, but once they got to high levels they were around for a long time. At least they were in our games.
There was no actual cap on levels like there is now-a-days. We continued to pull out our high-level characters, who by then were the heroes of their world, for years. So the time spent at high (named) levels as the majority of time spent for our characters. Rangers and Paladins didn't just have spells, they were casting them right and left. Not as much compared to the wizard of course (who was near godlike at those levels), but they were definitely casters.
Plus we had enough magic items to outfit a small army. Attracted followers were named and equipped with cast-off +1 swords and +1 full plate armor. New characters came in at 1st level (never mind that the other characters are level 23), but found themselves outfitted with ridiculous amounts of magic items. "Here, take this Girdle of Hill Giant Strength. I got a Storm Giant one!"
So yeah, our Rangers were expected to have spells. At least by the time they got up to a level where you didn't expect them to die off due to a bad roll.