Yes, list building is important to building something sustainable though many fail at building a well monetized list. In my opinion building a list is very much like building a blog. You have to niche down to something you can post good relevant content in a niche that can be monetized. Essentially every email in your autoresponder is a "post" and should give good content and a recommendation (affiliate link). Just like a blog, you have to produce good valuable content to send out in a niche you know well. It is easy enough to get people to sign up. To keep them, and have them buy stuff, is a whole other ballgame. Especially if they sign up interested in the traffic clickbait you use then you switch gears on them and send them stuff they may not be interested in. This is why the more successful email marketers have their lists subdivided - A list for MMO people, a list for health people, a list for diet people, a list for exercise people, etc. and send each list valuable content for that interest along with recommendations and such.
Sending people interested in MMO diet stuff usually doesn't work well in the long run.
Most of the list building I see done are "one trick ponies", the clickbait is for a single program and they have one or two emails for it then not much or you get hammered about the single program with the same emails every day. Like, if they haven't bought yet - I will keep sending them emails until they do. Of course there are the ones who try to use their list to promote everything under the sun and just think sending the "next shiny object" email will get them sales.
Just think about the lists you stay on and why you keep reading them. Also think about the lists you don't stay on and why you unsubscribe.