The free/proprietary distinction is only irrelevant for small-ish projects, on the order of a few months, where "good" is a one-dimensional measure in terms of features the application has: The risk of the software maintaining company being bankrupt in this timespan is low.
A typical mid-level employee at a company might be very happy with such tools, especially because they are usually new & shiny too.
Now imagine you are part of a team that wants to solve BIG problem, over a LONG timescale.
Suddenly the picture becomes more nuanced as software features aren't the only thing that matters anymore.
Would you really want to make the success of your project dependent on a third-party software company whose objectives aren't aligned with yours and that can take the tools you use away from you on a whim?
FOSS makes a very strong point there. The interface may not make you cry and melt your eyes with shiny buttons, but you can be sure that years down the road the software will still be there and you can read your old files no matter what, as the file formats are open. You can depend on the software, and,.more importantly, you can assess and proactively mitigate the failure modes in advance!
(E.g. the tex files from the 90s that you can find on some researchers website can still be compiled today; I imagine the entire research community would be significantly hindered if they would have to deal with the zoo of formats of proprietary software, rtf, doc, docx etc. In this sense FOSS can even act as the catalyst for establishing a standard, as is the case for tex files in domains of science.)
Though I agree that for image editing specifically, typically projects are probably not longer than you few months, so in this you case I imagine you could go without issues with the flow of new and proprietary software.