Number of skillsThis is very different than to what I remember from many of the systems that I played 30 years ago. Those classes had very few skills if any. I do seem to recall that the thief had a few skills listed on the level chart or something like that. Skills were not a focus back then.
In the 80s and early 90s several games caused skill explosion.
By the early 2000s, I count like 45 skills listed in the d20 3.5 game core. That is not to mention all of the derived manuals many of which increase the skill count dramatically. In 5e however, at the moment it focuses on about 20 skills, radically reducing the skill proliferation.
Another difference that I see is the way that skills increase.
Skill IncreaseIn the basic game that I remember 30 years ago, the few classes that had skills had numbers written on the experience level chart.
Looking over 3.5, I see that they did not use the individual skills rank increases using skill points the amount which were based on the player character's intelligence score and class. There was also that rule to limit ranks to 4 ranks for class list skills and 2 ranks for cross-class skills.
5e now uses a level based universal proficiency bonus for select skills based on class, race, and path.