With respect to this point, I think the author is saying that it's a dated system that introduces a ton of potentially unnecessary link rot. Basically, there's a ton of unnecessary technical debt because there isn't a more automatic way to set up/maintain redirects and instead often multiple manual entries are added for e.g. common misspellings of article names.
I probably bias myself by being too used to the status quo, and thinking its better than it really is. As a computer programmer, i probably underestimate the problems with the complexity of wikitext - since after all, a user facing markup language should not be anywhere near as complex as a programming language but there are times where it does feels like wikitext is basically spaghetti code.
Anyways, cheers.
-wikitext unparsable - wikitext is a bit insane but there exists a parser called parsoid. If we couldn't parse it it would be impossible to make a visual editor
- most pages are redirects: not sure what the problem is.
-boilerplate text - there is a template system to have repeated text in only one place. Not sure what the issue is.
- he goes on a rant about no search without giving much context. There is a search feature based on elastic search (older versions were based on lucene directly). In my opinion its a pretty decent search engine (especially compared to most sites that make their own search). I'm not sure what the actual complaint is.
-complaints about wikidata - this is more political than technical, however "If wikidata was a company, it would not exist anymore, and you wouldn't have heard of it." seems patently false. Wikidata is pretty popular even outside of academia, and is used quite extensively.
- category tree being a graph not a tree - that's kind of unfortunate but what exactly is the problem here. Its a problem on commons, but i've never really seen how its an issue in practise on wikipedia. Complex categorization is being taken over by wikidata anyways.
Template ecosystem is complex - it could certainly be better, but the complexity here is a trade-off allowing more flexibility and allowing the system to evolve.
Inclusionist vs deletionist: no comment
UI design: perhaps a fair point here, although i do kind of like the stability of the current design. Most of the modern web sucks imho.
Moral failure: i dont want wikipedia to fix the world. That's not its role. Its job is to document, not to partake.
Viz editor not being enabled by default: i agree, although i think it was pushed too hard in early days when there was still kinks, but its long past time now.
To be clear, i definitely dont think wikipedia is perfect, i just disagree with some of these specific criticisms.