This hasn't been true lately. Python is growing ever more complex.
But, for people still working in "computer science-y" domains, I haven't seen the historical dogmatism lessen; in many cases people are digging in.
In other words R is wrong tool to use for building the software just from maintainability standpoint.
I've seen very complex R packages that have been around for 30+ years. They are actively maintained. Applying good design principles, unit testing, modularity - all that is very much doable in R.
And you will want to write software in R, especially if the purpose is to support the very activity of working with R packages and to expose the R statistical environment over HTTP. Case in point, the software I link to, in my comment above.
That's an interesting take; my experience has been (at least the community) is quite proudly dogmatic on the One Right Way To Do It, for all values of "It".
I also don't like Python, but I think for different reasons and perhaps a bit less than you.
Never used R, but I understand it to be quite fiddly.