No it's not, Loser is it's own thing that is totally separate from SP, it has practically no fantastical elements attached and mainly revolves around an interest conversation/NLP system based on collecting "topics" and using them in conversation with characters you want to alter the scores of to progress through their various forms/behaviour patterns/titles or w/e you want to call them.
SP is fantasy based as it's all about superpowers(who'd have thunk) and how the player uses them to get it on with girls.
While Loser is not associated at all with SP, the content isn't all that different, it still features both incest and sub+dom, unless you're only here for the superhero type content, you'll probably like it, fair warning though it's pretty grindy, but it's a Baal game, he makes you actually play the game to get the sex scenes(there are ways to bypass the grinding but you'll need to edit files a little).
As someone who's been around since SP was in RAGS, SP2 will actually be the third incarnation of SP, i don't know if SP2 is a strict sequel, another game in this world or a remake/partial remake. What i do know is that it won't be in ren'py as, much like RAGS before it, Baal has reached the point where he's forcing the software to do more than it can reasonably do, IMO largely due to feature creep.
