While I didn't find it necessarily boring, I do agree that it doesn't need a comeback if it's just going to run on again. A conclusion maybe, but not a continuation of its previous formula.
With SJ the time shenanigans and power and influence of Aku help excuse a lot of things about Jack's quest taking as long as it did, with SBT there are episodes of the trio shopping at the mall or attending Lance's little rock concert when we've been informed the King of Galaluna is being tortured around the clock and his subjects executed. There's some hand waves about the gate and the danger and all but it doesn't make me forget the discordant tone.
It just wasn't good form. The same varied entertainment was there I enjoyed in SJ, comedy, action, drama, all that but unlike Samurai Jack the whole was always very at odds with its pace and point. Nothing seemed to make sense or matter.
Worst of all they try to address abandoning Galaluna by having the group claim it's just too dangerous, even when they're fighting monsters and threats every other day on Earth anyway, and later just guess that the fact they're still being attacked means Galaluna hasn't fallen.
No that's not how war works. Titan with or without the King alive still poses a threat, Modula wanting it destroyed is an entirely separate thing from whatever he's doing on Galaluna.
If SBT ever came back it needs a rewrite. Parodying the themes and pace of mecha can only excuse so much. A good example of executing that format was Megas XLR.
Like Samurai Jack it smartly used time travel to make the premise and crux of the plot ever present but brush aside its urgency.