You are treating "better designed" as a single axis: the question should be "better designed
for X" given a
specific value of X. As an example, to take your feedback item "the mascot looks amateurish" <- the kind of quirky humor that the people who designed this project have, and are thereby are appealing to, actually likes that mascot. In the genre of programming languages, this is quite honestly very typical: that mascot is part of what makes it feel like a programming language "worth paying attention to" to people like me (aka, people who study and learn interesting programming languages).
Without taking into account this context, your feedback is frankly about as closed minded and generally insulting as claiming that XKCD (or hell: anything by Don Hertzfeldt, which is probably an even stronger extreme case) is poorly executed because the artwork is likewise "amateurish" to someone used to full-color 3D rendered 60 fps animation (or hell: an actual HD video). However, these people have managed to entrench an entire genre of art that now others try to invoke in their own audiences.
Personally, I find the git-scm.com website to be full of way too much clipart and not enough personality; to the extent to which there is personality, I might call it "Web 2.0 with a hint of retro-corporate", which is highly awkward as I have always felt git represented something grungier, certainly "harsher": tied to ideas like raw power and distributed anti-disestablishment as opposed to control or simplicity. However, someone liked that website, and apparently you do. I find http://darcs.net/ much better at first glance, for a version control tool.
The original author (edit: apparently, also you) even liked the Firebase website, which has always turned me off as something designed to attract people who don't know what they are doing: it feels too "Web 2.0" and has much too strong an emphasis on "nothing to something" as opposed to "something to something great" to be a product to which I'd trust storing my data. Of course: I'm not in their target market, as I don't need their service and in fact "know too much" and can nitpick how they built it; they are targeting people who don't know enough to build backends, and that design thereby probably works for them. I thereby can't negatively judge their website without paying attention to that context.
tl;dr different strokes for different folks