I've been playing everyday for the past year, trying to get all the achievements, and ESO is always packed. So much so that it still lags the servers. Also read that ESO picked up another 2.5 million players just in the past year (not free trials). I don't know about 76, I won't touch it.
Over on Xbox One right now, ESO is at #25 on XB1's most played games list. To put that into perspective, ESO is ranked higher than DICE's Battlefield V, which released just a half a year ago.
Meanwhile Fallout 76 is ranked at #35 on the list, and is ahead of games such as Halo 5, SW Battlefront 2, Warframe, Gears of War 4, and Battlefield 1.
Basically both games are still quite popular and aren't going anywhere anytime soon. Fallout 76 will likely climb even higher on the list after the Battle Royale update and the NPC updates later this year. ESO might climb some as well.