In addition to what you rightly said, with different abilities that for unknown reasons have remained almost unchanged in dynamics despite 20 years having passed, the greater problem is that the fantasy class of the warlock was totally altered at a certain point, and unfortunately the warlocks themselves have made their own the wrong concepts that the developers have created.
I am referring to the concept of the “tanky caster” and that almost all warlocks repeat continuously, after having convinced themselves that it is so. In reality, at least for those who have played the warlock from its origins, the warlock was not tanky at all.
Affliction was very fragile and mobile and was supported by active and passive self healing.
Destrucion was the prototype of the glass cannon, with an emphasis on direct damage and very low defenses and decent mobility.
Demonology was instead the true tank, with a soul link that initially worked at 50% damage reduction (and with 5 talent points in master demonologist and using the voidwalker you had an additional 10% physical damage reduction) with more modest damage than the other two specializations.
What do we have now?
Affliction has lost all active and passive self healing, drains are almost non-existent, dots no longer apply pressure, and malefic rapture is a spell that patch after patch becomes more and more dominant.
Destruction is a chaosbolt-centric spec where the rest of the abilities produce really poor damage compared to the past (conflagrate has only served as a buff haste for years, but in the past it was truly devastating), shadowburn is a piece of cake, immolate would still have cast time if there wasn’t hellcaller (hero talent abomination in destruction optics). In 2025. A second and a half. Without dispel protection. With all the destruction synergies revolving around immolate.
Demonology is the one that comes out best, leaving aside the age-old issue of metamorphosis. Only then the absurd emphasis they often put on classes makes it an exaggerated spec in the number of demons summoned, but that many accept because “demonology is master summoner”. Which does not mean anywhere that to work it must summon 75 demons, but now the equation “master summoners = many demons” has been created. As if a “blade master” rogue had to walk around with 1378 knives. I would prefer “few but good”.