Ok... presuming that enough merits are received (achieved), which would be 1,000 for Legendary, the ranking up of legendary is still within a range of activity level, so yeah there seems to be random luck between activity levels of 784 and 1,030, yet once the activity level is above 1,030 the ranking up to Legendary is no longer random but is guaranteed as long as the merits are above 1,000.

I recall that in my own ranking up to Legendary situation (in 2016), I ranked up somewhere in the supra 1,000 activity level, so I perceived myself to have had been less lucky than some other members who had ranked up with activity levels that were below 1,000.

But, yeah these days, the other challenge is getting enough merits in order to not delay since the activity points are a bit easier to achieve by averaging 1 post per day and at least 1 post per every two weeks, within each activity period.