I had never read anyone with inside knowledge confirming this before, but I arrived at that conclusion long ago.
A rather extreme example of this lack of coordination is how Illustrator and Photoshop word their respective object rotate/flop/reflect menus.
Even though the functionality of flopping an image is the same in both, the menu positions, wording and settings are completely different for each. For example Illustrator’s Vertical Reflect does exactly the same thing as Photoshop’s Flip Horizontally and vice versa.
If the terminology conflict I just mentioned wasn’t obvious, the two respective teams have 180° opposite interpretations of what the words “vertical” and “horizontal” mean. This confusingly opposite terminology has been like this since at least the mid '90s.
Recently Photoshop changed the way it does and doesn’t constrain image proportions when resizing objects, but Illustrator did not. As a result, Photoshop, by default, constrains the selected object to proportional resizing and only allows non-proportional resizing when the shift key is held down. Illustrator does this in exactly the opposite way, where the default is non-proportional and where holding down the shift case constrains the resize to being proportional.
One thing I like about the Affinity Suite is the consistency and integration between their applications. Sometimes things need to differ due to the applications themselves doing different things, but at Adobe, despite the big three — Illustrator, Photoshop and Indesign — needing to work closely together, the Adobe teams seemingly don’t even talk to each other.