I usually save web pages as XPS or PDF, so I can compare the lengths. XML 1.0 specs is 56 pages; by contrast, YAML 3.0 spec with similar formatting is 96 pages. And XML specs describes both the serialization format and simple grammar-based validation for the resulting high-level language (DTD); YAML only describes serialization.
XML is relatively verbose, but this is by design and is clearly stated as design goal #10: "Terseness in XML markup is of minimal importance."
The grammar for XML serialization itself clearly has 1-character lookahead structure, so the parser must be deterministic and thus work in linear time. The tools that process XML (e.g. XML Schema, XPath or XSLT) are based on tree automata and, in most cases, work in linear time as well. (Of course, one can end up with a slow XSLT, I meet them all the time, but one can end up with a slow regex too.)
XML Schema provides very good types and a way to define your own types. I admit this part is relatively complex, but I think it's inherent complexity. If you have a Schema-aware parser, you'll get all the usual types (numbers, dates) and even more so, plus a better (more powerful) formal description of the high-level language than DTD. (For example, DTD requires all structures to have different names, while Schema can define context-aware types.) And Relax-NG is even more powerful. This extra description power doesn't increase the runtime complexity though, it's still linear time.
I don't know what you mean by namespaces being ineffective or vulnerable; I'd say it's as good as it gets for an extensible framework of roll-your-own languages without central authority.
The structure of a particular XML-based format (i.e. tag names, use of attributes, etc.) is the responsibility of the author of this format. Yes, some are very sloppy and illogical, but a lot of code is, regardless of the language.
I agree about huge arrays; XML was never meant to handle them. But modern tools perform very well on moderate and even large amounts of data; a few hundred megabytes is not a problem at all.
XML is not just plausibly reasonable for word processing or web documents, it's the only format designed to handle such (mixed) content.
There is some shortage of tools, most state-of-art tools now are Java-based and this doesn't work for everyone. But the biggest problem with XML is the amount of FUD and prejudice that accompanies nearly every mention of it.