It's a problem with KindleGen*. If you were to do your .ihatemobi class, it would work perfectly well as things can be styled multiple ways at once. You just can't have multiple separate class instructions for styling them so, at least not all on the same tag.
The only Mobi conversion tools that I'm aware of are
- KindleGen (including the Kindle Previewer variant)
- Mobipocket Creator (with all the limitations of KindleGen and more!)
- Calibre
- Mobi2Mobi (does not handle Unicode, your book will have to be in Windows-1252 encoding and use escaped entities for any special characters)
- the Perl Ebook-Tools package (front-end wrapper for mobigen/kindlegen and other command-line converters)
- Stanza (pitifully bad as a simple e-book reader, consensus seem to be that its conversion produces crap)
Unfortunately, I guess you have a choice between ceding control to Calibre, or cluttering up your source to compensate for KindleGen†.
* Now, if you were to try and indent a right-hand margin and failed, that would be totally Mobi's fault…
† Don't forget that newer versions of KindleGen add bloat in the form of the complete source files to your Mobi and you should use
Kindlestrip to fix that.
On the other hand, at least people would be able to admire your handcoding work?