$13k lens + $4k camera is pretty high-high-high-end. I know some people spend a bit on their hobbies (e.g. RVs, ATVs, high-end rifles, etc.), but $17k (probably more like $25k with the other lenses you'd have) is a lot.
I'll confess to skimming through the Northrup video review of the two lenses. They thought the 200-600 compared well (on the a9) for a fraction of the price. Anyway, the 200-600 is on my to-rent list one of these days.