Do you have any reasonable argument about how the transition between the first real self-driving truck¹ being around and more than 90% of the trucks being self-driven could take more than 5 years?

The only way I can imagine it would take this long is if governments just prohibit it. Even then, they'll get a big chunk of the market in 5 years.

1 - By real, read commercially available, that can run into any reasonable road without anybody inside.