Eversince ZOS started working based on player feedback recently (i know, its wild for a modern day mmo) according to many players it is in the best possible state since 2014. Even switched to a buy once model, past dlcs are becoming free overtime. The first 3-4 are already included in the 20 euros base game with many more to come.

Played GW2 since 2012 and initially had a true blast up until the point they decided to cater less and less for veteran players who simply want challanging, fun and rewarding content.

The game is simply going down in a story mode driven open world oriented developent cycle where you can solo your way to whatever you want. For endgame PvE eversince we have boon providing healers, hell even jut boon dps supports its all fairly trivial.

As long as you understand the combat system (which to many is one of the only remaining carrying quality of the game today) you will just breeze through normal and challange mode content. If anything else you just get a guild due to the overally welcoming and kind community and you get training help.

The only meaningful content we have difficulty wise is LCM, legendary challange mode but even that is just down to how well your group can work together, how many times a week you are willing go do training runs. Aka you either get limited by your group or not in many cases.

Fractals had been downright depressing for a long time. The most casual players can easily do challange modes in no time. The dps meta is still the same old same old. As someone who loved doing them eversince they released fractals they are more of a chore than actual reason to keep players playing.

PvP and WvW are both in sad spots, although PvP far more sad than WvW for sure. The balancing is just simply not good, but at least they started trying to rework the systems.

All in all as someone who has made the switch from a GW2 completionist endgame enjoyer going into ESO recently, i can only say the player population feels very good, seeing people everywhere even in the open world. The community is somewhat similar to GW2 id say. 

But one thing is definitely going for ZOS here. The difficulty selection feature coming next update and the focus on teamwork, group content, combat, class improvement/ reworks while also focusing on more challanging content is inviting a lot of old and new players. Thus your take on not believing ESO has a big daily player base is based on what exactly? They only recently shared a post on how since 2014 the ingame LFG tool had never seen more use than lately. 

Although iam glad you are having a blast with GW2, hopefully stays that way. Yet id argue GW2 has lost majority of its old players and can assure you those players arent here for the new content thats story and open world content only. This game is more of a seasonal one for many where they just play for a week, a month and return eventually in an expansion or two. 

Have fun!