Do what you do and what you want. I will just not follow the same path. The real importance is to know why we are, individualy doing it for.
For me, curiosity.
halfalp, you might well be right, although the specific hypothesis that living Z2103 originated in the Steppe is untestable through ancient DNA, and is thus what Popper defined as pseudoscience - a matter of instinct, much like the tenets of psychoanalysis, a belief in God or interpretations of literature. The only objective methods of testing this are currently using variance analysis on modern DNA, and they yield a slightly different alternative 'most likely' answer. But all might change as the data accumulates.
There are four basal branches of living Z2103 - three of these branches are estimated to be wholly of a South of the Caucasus coalescence (PF331, Y13369 and Y4364) and the fourth is estimated to have a Caucasus branch (CTS8966) and a Steppe/Eastern European branch (Z2109). The only steppic branch appears to be a sub-branch of a basal branch, and this sub-branch Z2109 shows little or no sign of migrating back South of the Caucasus at any subsequent point.
The Steppe looks from the data to be at best a tertiary development of Z2103, with any migrational separation across the Caucasus occurring at an early stage (whichever way it occurred), long before the late Bronze Age steppic migrations into Southern Asia. Accordingly, I would suggest these late Bronze Age steppic migrations were of people that were predominantly R1a-Z93 (rather than R1b-Z2103), albeit with probably some Yamnayan-descendant admixture.