[jocampo]

Without engaging in the "format war" discussions and being strictly technical, epub can do basically the same. But like you say, for pure text books you will not notice major differences between that and epub or even mobi.

The main problem with FB2 is that is an old format and the best ereaders on the market do not support it natively; you depend of Calibre to convert, that's an extra step and not an advantage in my opinion. Most commercial online bookstore do not sell books on that format either (commercial, not free stores)

Images are also converted to to base64 making the end file size bigger. For technical books or manuals with lot of images you will produce a much bigger file per book. Multiply that several times if you have hundreds of books and your internal ereader memory or SD card won't hold the same amount of books, something you can avoid since the very beginning when using one of the common formats. Paragraphs are also heavily indented.

FB2 is also slow for big books (I tried already, long time ago) freezes when loading a book or takes too much when turning pages. This is because FB2 is a monolithic format, so the whole book needs to be loaded into RAM to read.

To be fair, reading basic eBooks/novels, specially if they are not too big or filled with graphics FB2 is more than enough, you are correct. And for you, the reader that you own, your needs and the type of books you like, the best format is the one that works best for you!