I agree with this point. Writing that sort of sentence is meaningless fluff.
That being said, you need to think of things from the position of the people hiring you. The manager is going to give the tech lead a bunch of resumes and cover letters and ask them to read through them and make a short list of 5 (or whatever) to interview.
If they are looking to hire someone to build RoR web apps with a ClojureScript front end, then you make the tech lead's job easier if your resume and cover letter highlight your experience building RoR web apps with a ClojureScript front end - or if you don't have that, at least point out how your other experience means you can still solve their problem.
While it is possible that a generic resume contains all the information needed to make a determination of whether you are qualified for the job, you should be emphasizing the parts relevant to the current job so the person putting together a short list doesn't have to study your resume, instead, they can look at your application for 30 seconds and go:
Yep, yep, yep, wow this person has everything we're looking for, onto the short list they go.
Because here's the thing. The tech lead is usually a busy person and they've got better things to do than spend and hour or two sifting through resumes.
When I've had to do it, I'd take a quick first pass through all the resumes and put them in one of three piles: easy yes, easy no and maybe.
If all the relevant information is in your resume but I have to hunt around for it, then you'll likely end up on the maybe pile.
If I get through the stack of resumes and my easy yes pile has enough candidates, then the maybe pile doesn't get a further look, because I'm trying to minimize the time I have to spend looking at resumes.
If you're using a cover letter to apply for a job, it means you have no human inside the company that is advocating on your behalf. Your friend wouldn't ask you for a cover letter (in most cases) if he/she was going to refer you internally. So when you are required to use a cover letter, it usually means you're applying to a job 100% 'cold' as an outsider.
Unfortunately that may be the case sometimes. If a cover letter is required, there are a few key elements
1 - prove to the reader that you actually paid a bit of attention to the job requirement. I spent 20 years in recruiting, and generic cover letters that clearly weren't written for me ("Dear Esteemed Employer") never got my attention. I want to know what interested you in this opportunity, or briefly what you know about the company (could be lots of things).
2 - Talk a bit about what you're interested in from a work perspective. What kind of work do you want to be doing (and hopefully that is the work we're offering).
3 - Maybe check off a few boxes from the job spec. If they require a degree and n years with Python, a few sentences to check off those boxes will make it easy for the reader (often a recruiter or admin with little experience and limited knowledge of the domain) to say yes to you as a candidate.
Semi-formal tone. You can link to GitHub, but usually I link GitHub and LinkedIn on a resume.