Sadly Mac's are all soldered in these days. My first Macbook Pro back in 2009 had so many mods, that I even took out the disc drive and used a special cradle to have a second SSD.

It isn't actually about the machine you use. It is about why they choose not to give your the tools you need to do the job. If they cannot afford it, how can you believe they will afford your paycheck, or even keep the doors opens? IF they refuse to give you the resources to do the job on your first day, what will happen when you need something else down the road? Or are they just trying to minimize their expenses and resources give to employees?

Using your machine "until I found out whether they were serious enough to properly supply the necessities." makes no sense whatsoever. They aren't. You don't need to waste any energy finding out, they fact that they asked gave you your answer.