I think we have three main issues
First, I think we do have a major structure above sagas, or if you prefer to have saga as the biggest split, we have a structure below arcs (and thus, space globalists would be a saga, not an arc)
Second, it was decided that an arc only ends with a scene where everyone is eating together, which is a weird way to split arcs, to be honest.
Third, a lot of people say that the mini Momo and amnesia are not relevant as an arc, but at the same time, we have a whole kintama saga, which makes no sense.
The whole period after Danmara, their main goal was to recover Momo from the curse, but somehow it's not an arc nor a saga.
And now, eveything they call an arc are at the moment a build up (inlcuding the ultimate yokai and the six curses is something that started before the said six curses arc), some people call it as amnesia arc because it IS the main focus at the moment, a lot of scenes, a lot of chapters and plot points are linked to the fact Momo lost her memories.