UO addressed SP as a problem and gained an audience. EQ addressed some of UO's problems and broke through to a larger audience. WoW addressed some of EQ's problems and broke through to a larger audience. Nothing since WoW has even correctly understood WoW's problems, and most have accentuated them precisely because they don't. Meanwhile Blizzard has let opportunities slip through its grasp with WC3 custom maps becoming entire genres independent of Blizzard, so it's not like they have the win button on lock.
You mentioned something above I wanted to address separately. When UO was released, I contemplated buying it since I had played some of the Ultima games. When I heard it was open world PVP where gankers and griefers could steal all your stuff, I decided against it. As you pointed out, EQ1 marketed itself as a cooperative PVE game so it attracted a much larger community of players compared to those who preferred open world PVP. While a lot of people played EQ1, a significant chunk of the player base was negatively affected by the design decison to force grouping for most of the content. A lot of players who had real life commitments were also prevented from participating in end game PVE raiding because the hardcore raiding guilds controlled who had access to the raiding content.
WoW's support of solo gameplay and instanced end-game raiding sucked away the large majority of EQ1 players, especially the more casual players with real life commitments, jobs, families, etc.
How does all this apply to TESO? ZOS as well as every other dev out there knows what the gaming demographics are. Unlike a lot of people here, they realize that everyone has different likes and dislikes. Some people prefer PVE, some PVP, some like to solo, some group, some raid, etc etc. If ZOS made one critical design mistake, it would be the mistake of trying to satisfy everyone instead of focusing on just one target demographic.
Cyrodil PVP was designed for the UO and DAOC fans. The levelling up experience from 1-50 was for the TES fans who enjoy the story/lore as well as the casual gamers who want the option to solo. The original veteran zones were designed for the EQ1ers who enjoyed forced grouping. That created a major shitstorm. One thing every MMO dev learned from the TESO veteran zone fiasco is that the EQ1 forced grouping model for MMOs is forever dead. The new generation of gamers, especially those whose first MMO
was WoW or something released after it, soundly reject forced grouping.
In other words, EQ1's demise combined with WoW's success combined with the outright rejection of forced grouping in TESO lead me to conclude that the EQ1 sandbox model that so many people here yearn for is NEVER going to happen again. You either accept a new MMO for what it is or stop playing them outright.
Anyways, the overall point is that TESO attempts to satisfy multiple target demographics at the expense of focusing on just one target demographic and being great for that one demographic. As a result, across the board it gets a grade of "average". The people who wanted a hardcore PVE raiding game, a hardcore PVP game, a hardcore single player game, etc are always going to be disappointed with the game.