2019 and 2020 books are in the
Odds and Ends
A Big F You
4 2, 7:05am
Yes Stallu are trolls/giants in Saami legends. However in some stories they are clearly talked about as if they were a people and predecessors to Saami. Finns had similar legends about mythical giant predecessors called Jatuli or Meteli, probably either learned from Saami, or developed independently from same origin. I can't provide an English source right now, however in collected folklore such stories can be encountered, for example in books of Finnish folklorist Samuli Paulaharju. Norse of course had their own legendary giants, Jotunn. The name is very similar to 'Jatuli' and possibly Finns loaned the name from Norse, however Jotunn are otherwise quite different to Finnish/Saami giants. I don't think Birkarls are related to Stallu legends, they seem too recent. Saami also had the legend of mythical invaders, the Chudes, and Birkarls and other tax collectors are much better match to that.
"Mythical predecessors" are of course very common in legends everywhere, and often they are mentioned either gigantic (to explain various natural or manmade rock formations) or small (to explain why they are never seen). So it's hard to say if large size of the Stallu/Jatuli means anything. It is very interesting that Inuiti predecessor legends talk about people called 'Tuniit' who are described as large, but not very smart, clear parallel to Fennoscandian stories. In case of Tuniit, they can be easily connected to actual archaelogical culture, the Dorset. In Fennoscandia it's bit harder. It is possible too that Stallu acquired traits from latter peoples (Finns, Germanics, Chudes) as centuries passed and old myths were mixed up. As said, 'mythical predecessors' are common theme almost everywhere. Sometimes it's obvious they were completely mythical (Titans), in some cases they may have been real but acquired mythical characteristics (Chudes, Tuatha de Danaan), in some cases it's easy to prove they existed (Etruscs).
Linguistically, Saami language has a strong substrate - layer of borrowed words of relatively recent origin which are not loaned from any currently known language. This has always been obvious but only in recent years it has been studied in greater detail, from example by Finnish linguistic Ante Aikio. These words were probably loaned something like few centuries BC, or 400-500AD latest, implying that that's when modern Saami expanded to Lapland.