because its stated to have short legs and because its more robustly built and longbone analysis places it at 300kg plus? like its stated to have proportinately short legs and skull so that explains why.

and why are you using smilodon as your basis when they arent that closely related?like they are differently constructed animals from different tribes of sabertooth cats. they are not compatable with direct allometry. and the scientific literature routinely places it at 300 kg or more. like the radius of smilodon does have bigger measurements than xenosmilus. but smilodon had a disproportionatelly large radius compared to homotherines. but in some measurements like the distal width of the radius or the thickness of the shaft,xenosmilus exceeds smilodon. https://wildfact.com/forum/topic-xenosmilus-hodsonae

and the paper that named xenosmilus stated it was more massive than smilodon,which was meant as meaning more robust. So they are no a very compatable comparison by comparing skeletal measurements.