In OD&D high level characters had more hit points, a improved to-hit chance, and due to acquisition of magic items, a superior armor class. Wizards and clerics had increased damage due to higher levels spell but all the other classes had flat damage curve. If it increased it was solely due to having a magic item. The difference between the highest and lowest values was not dramatic in OD&D. High level character could be overwhelmed through attrition.
Starting with AD&D 1st, the difference between the highest level and the lowest level began to increase. Non-wizards, particularly fighters, also improved how in much damage they did as well as enjoyed a improved armor class, more hit points, etc.
With 3rd edition the wealth of options increased dramatically for all classes. A trend that was continued in 4th editions. This was especially telling in the use of the open ended ascending AC. Both editions made it easy to push the armor class of high levels to point where a natural 20 was needed by most lower level creatures. Given the fact that the methods of dealing damage increased both in frequency and amount dealt this one-two punch meant that not even attrition tactics were effective against the highest levels.
The open ended scale was also applied to skills and other non-combat skills. Leaving higher level characters with bonuses larger than the +19 difference generated by opposing d20 rolls. This also led to effect where the difficulty of mundane objects became trivial high level characters. Leading to many authors to develop special variant of doors, traps, in the quest to find challenges for high level character. These variants were considered by some to push the limits of being believable.
D&D 5e in contrast caps the open ended bonuses of previous editions. An example is the proficiency bonus which starts at +2 at 1st level and +6 at 20th. Ability scores at capped at 20 when a character levels and gains a attribute increase. Monster to hit bonus and Armor Class are similarly scaled.
This result in a game in which the power balance is similar to that of the 1974 edition of OD&D. Although it is achieved by using a different set of mechanics and numbers.
The mechanics of the 1974 edition of OD&D were very minimalist compared to later editions. When players attempted as their characters to deal with traps, roleplay with NPCs, figure out mechanism. They had to use their own skills in conjunction with the referee rulings. The implication of this is that in terms of mechanics there was little that was different between characters.
This extended partially into combat where all classes started out with the same to hit chances and dealt the same damage (1d6) regardless of weapon.
AD&D 1st, and 2nd edition made the classes very different from one another. 3rd edition refined the flexibility introduced in 2nd edition so that just about any type of character could be produced throughout the 20th level of play. However this was achieved through the combination of combined specialized elements from classes and feats. Feats and classes themselves were highly specific. A pure fighter was very different than a pure Wizard.
The difference between the characters in 5e returns D&D to a situation similar to that of 1974 OD&D. However unlike the minimalist OD&D, the differences between characters are baked into the mechanics through bounded accuracy.
It can be basically summed up as Any character can attempt any actions but some are better than other at certain actions. A handful of abilities (like spellcasting, martial skill, religion, etc) remain the specialized ability of a specific class. Everything else, anybody can do.
In OD&D the everything else boiled down to player skill. In D&D 5e adds specific mechanics that can be improved through advancement. In the D&D 5e Basic Set this is mostly due to the choice of proficient skills and what ability gets increased. This produced a dynamic that is unique to 5e.
- 2nd edition every character could specialize through kits as well as classes. Kits often focused on non combat abilities.
- 3rd edition every character could either specialize by taking repeated levels in the same class and specific feats or they could become generalists by taking levels in other classes.
- Each characters has specialized abilities as a result of their class but are generalists otherwise.