Played EQ from a bit before initial launch all the way up through Secrets of Faydwer I think was the final exspansion I bought. The Serpents Spine exspansion was probably the last one I would really consider myself actively playing though.
I'm not trying to say that there weren't countless ways to get ahead of other more average players or that there wasn't anything that required skill. I just don't really agree with the notion that the actual leveling itself was any harder in the old MMO's like EQ than any other modern MMO. There were countless other mechanics running tandem to the actual exp gain process that could be annoying and or set your progress back but they didn't make the actual act of gaining exp any more difficult.
I don't know maybe my experience was different from other peoples or something because outside of the very initial time period when no one was high enough to have the higher rez spells yet I never had any issues getting rezzed. There was always someone i knew to come rez me or someone in my guild to do it. Corpse runs were very easy as well when I had necros to summon or monks and necros to drag the corpse to a safe area. I wasn't so totally reckless to die somewhere where it would be next to impossible to retrieve my body without having a contingency plan in place though.
Even then I still cant bring myself to find those kinds of mechanics difficult because I never had the slightest trouble with them. There were some times when I found them annoying and some times I would have rather not had to deal with them but never did I actually find they made my experience playing the game more difficult.
On the invis and sneaking front I was a Ranger so I could cast my own invis spells and I got speed spells fairly early on so to not die every time my invis dropped. At the lower levels I kept my sneak skill as high as i could manage which helped alot. Undead were pretty easy to spot from far enough away to avoid them and Conning anything else would tell you if they saw invis until you managed to remember where that stuff was.
I guess I would say that there were plenty of ways to use your skill as a player to make things far more convenient for yourselves but it wasn't required because the actual combat itself was incredibly easy while leveling. None of the mechanics that were there to hamper player convenience managed to make the actual combat more difficult which is where the vast majority of your time leveling was spent.
Getting exp was a lot harder. First, there was the basic leveling rate. It was far slower. I played obsessively the first week, dozens of hours, and got to like level 9. The sheer number of hours needed to gain a level puts today's MMOs to shame, except perhaps for some super-hardcore Korean stuff. Part of that is because of how long the battles were, much more "auto attack and wait" and gradual depletion of health bars, especially at early levels.
Next, there was the difficulty of enemies essentially forcing you to group to level efficiently, as xp loss on death (talk about a different era) was hours' worth. And just looking for a group could take hours if you were say, a ranger, and didn't have a large guild with members around your level with room for you (and this is one reason EVERYONE joined a guild - it was so hard to get by without one).
Xp from quests was negligible, and quests weren't all that common anyway. Traveling took ages. Meditating with the damn spell book in your face took ages. So much down time.
Mobs weren't organized into nice discrete encounters; they were messily clumped in ways that could give crowd control-less groups (which were very common for the first year, at least, because crowd control classes were not popular) fits, and in open areas, they wandered along a complex combination of paths, often resulting in "adds" that were difficult to avoid. Soloing and got an add? You're usually screwed, without SoW or some form of crowd control. And escaping from combat for many classes was not really a viable option: if you were losing the fight, you were going to die. Remember the walk of shame when you'd lose AGI at low health?
Meaningful item upgrades were very difficult to get, aside from basic crafted stuff, like banded mail.
Organization was extremely difficult with the lack of social tools that we take for granted today.
Hybrids (ranger, sk, paladin) for the longest time had a 40% xp penalty for no stated reason other than their popularity, and some races (Trolls, Ogres, maybe others, I forget) had their own penalty as well.
Summon Corpse wasn't even in the game, initially. If I recall, that was added with the Splitpaw zone in response to players upset over silly things like months of work lost when they, naked and mostly helpless, weren't able to recover their corpses within 7 days, and all their items poofed.
And corpse runs...bound in a city (as all non-casters had to be), and having to spend 30 minutes running back to your body? Brutal. Especially if you, now naked and helpless, got killed again on the way. And corpse poofed after 30 mins because it was empty, making rez impossible.
Yeah, I'd say leveling was more difficult.