Photoshop vs. Illustrator. Is There An Industry Standard?

When I was first getting started in surface design, I thought Illustrator (Ai) was the industry standard and I went on a path of creating an entirely different style that would work well with Ai.
My style is painterly with lots of loose strokes using watercolor and gouache and it did not work well with Ai. I was able to vectorize my paintings and it looked good (see image on the right, above), but it did not retain the textural strokes that I loved to see in my final patterns.
I went down the rabbit hole of finding out more about PS and turns out, LOTS of designers work exclusively in PS and get licensed as well!

Nothing against Ai, I love the ease of pattern making in Ai and I do use it from time to time but now I mostly work in PS and all the times that I've been licensed, the designs have always been in PS!
 

So, figure out your medium of choice, learn one program then tackle another but know that they both are industry acceptable!