Based on what i read the comments you look like you are a streamer/youtuber and one that the sub likes but based on what i read in your post since i don't know you and i don't bother with youtubers/streamers here is what i think:

High dragon trials are considered to be the endgame content. Your main question is what to do with the game afterwards which the only obvious answer is wait for new stuff or if they bring another type of content. Dragalia seems like a mainly farm game where you need some luck to get the good adventurers and tackle content cause f2p wise there is no good f2p dragon (i don't consider the high dragons f2p) and as far as adventurers go only very few can play.

Moreover, the part of your post that was more interesting so i thought i could reply was this:

Came back and while player quality has increased, stupid mistakes keeps happening and nothing ever gets done.

Do you mean that the whole party does mistakes or do you mean that you are superior and the other make mistakes? Because if you think the latter sorry man but you disgust me as much as those elitist guys on discord. Meaning, some guys(it's true) around here think they are like super good while they trash the rest of the community. Noone is perfect is the answer that you are looking for also patience is a virtue i have read countless posts through out the reddit and they said that they took longer than you and succeed. Now if i don't get it right or you mean that you don't like the state that the game is then you can talk with your viewers what it could be done or changed to be more appealing to you and to the other players and since you promote their game i'm quite sure that they would listen to you.

Also, since we aren't so sure what the new content will be it's a good idea to wait. For instance if the next gala is elisanne mark my words she is gonna be as broken as gleo due to the fact that she is loved by cygames as much as cleo both having no bad forms so would that be more appealing to you? Imo if you are bored e.t.c you can always find another game and launch dragalia when it is interesting to you or make your channel(if you haven't done already) more like mentoring one if you like for instance.

Thanks in advance.