>I test the linux machines are dev machines just used for compiling/testing and basically have shared passwords, or they're servers for webapps or something else where normal users most who have a windows machine won't have a shell account.

And you don't actually pentest the software which those users on the windows machine are using on the Linux systems? So you find a Jenkins server which can be used to execute Groovy scripts to execute arbitrary commands, the firewall doesn't allow connections through port 22, and it's just a "well, I got access, nothing more to see!"?