It’s important to fully believe you’re hot shit and companies pulling stuff like this are getting in the way of your professional growth.
Asking for what you need to do your job is an important skill. If you have options other than this place of employment, it might be worth practicing.
Because working slowly will also look poorly on you.
To put it bluntly, you are screwed where you're currently working. If they can't prioritize a decent machine for you to work on, then they really don't value your work as a developer. (Most likely, they don't value any developer's work.)