You're mixing in some stuff, that aren't really Semantic Web related.

RSS vs. Atom was less about the Semantic Web than an squibble between different XML formats, one very loosely specified, the other more ... well-formed. The Semantic Web did had a small foot in the RSS wars - the very first RSS (RSS 0.9 from Netscape) was RDF based and for a short time RSS 1.0 wanted to rebuild RSS on an RDF basis for the expandability of the Semantic Web, but the later discussion were about the XML variants of RSS and then Atom, wether the spec was adequate, wether it was frozen or how and wether it should be fixed, etc.

The XHTML discussions were less about elements in my recollection but about parsing models. XHTML reformulated HTML als XML which meant an error model with no error correction but failure on the first error. And XHTML 2 tried to evolve structural elements by being not backward compatible but defining a somewhat different new dialect. The backslash against XHTML was against that, a group sponsored by the browser makers then formed which wanted to evolve backwards-compatible and to standardize the parsing of tag soup → HTML5.

(„Semantic elements“ were often a shorthand for „instead of a dumb div use the appropriate HTML element. That was more the quest of the web standards project than the Semantic Web.)

(Slight overlap: How to embed Semantic Web statements has a small relationship with XHTML - RDFa started imho in an XHTML 2 module.)

I somewhat miss that time. All these bloggers with an interest in web standards and how to do them best had their own idealism and the cross blog and W3C discussions were always interesting. Today web standards don't have that publicity and idealism anymore, they seem more like an engineering collaboration of the 2½ big browser makers which get to decide among themselves. Maybe it was always so, but it seemed different at that time.