Somebody correct me if I’m wrong, but the problem I think is the 1-hour limit per mission.
There was this other mission wherein you get 2 cubes but takes a bit longer compared to the Siauliai one.
There was also this one where you can fight more than 4 bosses but again the 1-hour limit makes it not worth it as the bosses seems tougher compared to the 1st mission.
If you have a good pre-made party, then the other missions might be worth trying for a change, perhaps getting even better exp and silver.
When queuing though, Siauliai seems to be the safest and fastest to do within the time limit, even without having tanks nor healers.
A simple question to ask why would be: Do you want to do a mission in 30 minutes or less with decent exp and silver, or one that would take you nearly an hour with a slight increase in exp and silver?
Most would go with the first, considering missions aren’t the only thing in the game where you can get exp and silver. Your time is better spent elsewhere.
As for the other missions though, I think they need tweaking to become considerable.