A main reason why 1e Fighters were "fun" is because they were simply overpowered. 1e Fighters are strictly more powerful at low tiers. When a game gives more power to one player, that game is more fun for the player, but less fun for the other players. Anecdotally, at least one fourth of 1e players played Fighters, but probably, it was more like over half played Fighters. In 5e where there is more class balance and more classes to choose from, perhaps only about 6% of players play a strictly nonmagical Fighter into high tiers.
Dejure, the 1e situation reversed at the highest tiers. But defacto, the 1e ad-hoc, disparate, mechanics caused the entire 1e game engine to fall apart at the high tiers. Perhaps the 1e Magic-User players could enjoy a brief reprieve from levels 9 to maybe 12 or so, where the game allowed some sense of equality with 1e Fighter players − perhaps even an edge toward the end. After that, only a few 1e tables managed to homebrew houserules that could play sustainably into the higher tiers. For most, the game ended too soon.
For many players accustoming to the low tiers, the "traditional" D&D "experience" is one of Fighter class supremacy. There is an ongoing tradition of resentment against high tier spellcasters and low tier cantrips because they displace the entitlement of the overpowered Fighters. It is as if the Fighter "deserves" to be in power, and spellcasters "deserve" to suck at low level and "deserve" to have their high level spells removed.
The 4e and 5e development of class balance came with other sentiments. 3e systematization made it possible for more players to advance into the high tiers. So 3e spellcaster players began to accustom to their own supremacy of spellcasters. The socalled "CoD-zilla plus Wizard". The "C" Cleric "or" "D" Druid got a taste of power sooner if they turned "selfish" and reused all of their extra magic that was meant to buff teammates to buff oneself instead. But eventually at the highest tiers, the amassment of Wizard spell slots and their strictly more powerful spells at each spell slot, as well as the fact that most spells automatically became more powerful while advancing at levels − allowed the 3e Wizard players to outclass every one else − if ever reaching those highest tiers.
Where class imbalance was the "thesis" during 1e, 2e, and 3e, the "antithesis" is 4e. 4e design had all classes employ the same mechanical gaming engine with strict balance at each level. 5e is the "synthesis" in the aftermath.
5e design prioritizes class balance during combat. But it allows disparate mechanics that can cause problems similar to earlier editions. Also, class inequity can resurface unconsciously, such as 5e Wizards remaining subpar in combat encounters in the lowest tier, and the lack of magical utilities shutting down 5e Fighters in noncombat encounters.
Even so, 5e class balance empowers cantrips, higher hit die, and AC spells like Mage Armor and Shield, so 5e spellcasters are competent in combat at the lowest tiers. Meanwhile at higher tiers, 5e spellcasters are significantly less powerful. The spells no longer "autoscale" and require the expense of higher slots for any more powerful effect. There are far fewer high level slots at the highest tiers. "Save or suck" spells that autowin a combat encounter are rare.
Meanwhile class balance designs the 5e Fighter with the same design space that caster classes uses. The 5e Fighter is extremely powerful in combat encounters. However, the lack of versatile powers makes the Fighter incompetent at high tier noncombat encounters. The pressure to form more equitably in noncombat encourages Fighter players to want to trade combat supremacy for more powers that are effective out of combat, that necessarily feel more magical, such as flight, teleport, and so on. Thus the low tier "Batman" starts to feel more like high tier "Superman".
