Honestly, cover letters are something that needs to die out for most jobs, they're entirely pointless. 99% of the time, it just seems like they want you to rehash the contents of your resume and grovel a bit for the company. Screw that.
You want someone with 5 years experience in a role, my resume shows I have ten years doing that job, make your call if it's good enough to interview me or not. I'm not writing an essay about how excited I am for the opportunity to count widgets at your company, and how it's always been a dream of mine to work inventory control for a company that changes the world by ensuring stock buybacks can regularly happen by overworking and underpaying their staff.
Biggest waste of time I see recommended for applications. I don't apply to any job that requires them.