I'm not familiar enough with early medieval military history to know the ins and outs of this debate, but theory seems obviously falsified by the fact that chariot technology in other time periods did not result in such a feudal system.
Scholars have written scores of papers and spilled gallons of ink on both sides of the topic. What do you know that they don’t?
I think the theory is wrong, or at least incomplete, but the evidence against isn’t as clear as all that.
For a similar example from another field, observe the decades long contention in epidemiology about droplet sizes and viruses like the flu and Covid not being airborne, in contradiction to basic aerosol physics.
In fact, if you are right, you should write up a paper. There are numerous journals that would be thrilled to resolve this controversy once and for all.
The reason they spread so quickly from the Eurasian steppes to throughout most of Europe and Asia was precisely because they were so dominant. As a matter of fact, not only did the chariot spread, but the horses the Sintashta culture and its immediate daughter cultures bred to best PULL the chariots spread with the chariot to the extent they are the ancestors of every single domestic horse in the world.