[F6 Hawk]

Let's assume the data you provided is accurate.
As zroger stated, the 6-speed service is roughly @ 45K miles, then every 30K miles thereafter. The 9-speed is every ~60K miles.

Based on my driving history, I will keep my Ridgeline for 170K-175K miles.

• The 9-speed would require 2 ATF changes @ $360 = $720
• The 6-speed would require 5 ATF changes @ $150 = $750

And many 6-speed owners, including yourself, change the ATF much more frequently.
You've changed yours at least 4 times before reaching even 60K miles, so $600 in dealership costs.

With the 6-speed, you can easily DIY a ATF change. With the 9-speed you can't (easily). So cost for 6-speed change is less than $40.