First, welcome to Security Stackexchange,
In trying to make the case to these people that WSL isn't a threat, I
see conflicting things online. Google "WSL security" and you come
across articles about bashware.
The fact security experts and other It professionals are in fact talking about WSL and that it was developed in conjuction with (among others) cannonical (the guys that brought you Ubuntu) is in fact showing that there is a good and proper security climate around WSL. a Better one than is around just Windows. (IMHO)
Apparently a hacker who has gained
access to a system can run WSL, install wine, and use it to install
This is true for any 'hacker' that gets access to your system.
Also you do not need
wine to infect the windows once your inside the WSL.
Linux has a proper permission system in place, one you can leverage inside your WSL. (things like using sudo and limiting how you can sudo and who). Also Linux services are constructed (mostly) on a least amount of permission bases. an average there more secure than windows services due to that basis.
You do need to learn more about how linux and the WSL work and how they interact. The company would be wise to expend there knowledge and start (on limited scale) to learn about what WSL is and how it works.
The main diffrence for you between a Linux system and a Windows system is how much you have worked in it. Working in WSL allows you yo learn more about linux and its security systems without sacrificing your windows basis.
As always knowing more about computers and computer systems makes you better in security, getting exposed to different paradigms makes you think about diffrent possibilities.
I would recommand any company (worth there salt) that operates in an environment where security matters, (so everywhere) to learn and get hands on expierience with Linux and the WSL is the best way to get started with it as it has the lowest barrier of them all. This expends from them tall the way up to end users