Most Samsung nexus htc? LG modern android devices worth giving two shits about went the single partition route for everything outside of the OS
The important thing to note is that the S2 comes from the pre-ics era of android phones where basically everything was a mess, manufacturer skins were extremely demanding of what little hardware those phones had, storage was practically a mess, and there was even a version of android done only for tablets because idk why.
The storage partition is just a remnant of that era. The bigger question is why you went for a nearly three year old phone when there are better options for the same price.