I'd say that, if you are the kind of player that DOES have the skills and chops to reharmonize a piece (
deliberately! accidents don't count!

) every time you play it, sure, a songstyle gives you a lot more flexibility.
But, let's face it, the song itself usually defines the chords, and the style has only a mere 4 fills to chose from, whereas an SMF, every fill can be different in some way. And most arranger players are happy enough just to get the changes right in the first place, let alone throw in a bunch of tasty (or not!) altered chords and substitutions...
Perhaps for jazz, the songstyle is a better solution, mind you, jazz players will want to get as far away from a rote playback of the record version, so a songstyle wouldn't really be of much use. Not to mention that most songstyles are for well-known pop and dance hits, and your audience isn't really going to
want you to go all Keith Jarrett on it!
Overall, I don't think I use a single songstyle in my song list. If I need something close to the record groove and feel, I'll use an SMF every time. But that doesn't, thanks to the Mark/Jump feature, mean I'm giving up on structural control of the song, and, just like a REAL keyboard player, I now have two independent hands that can substitute all I want to (or can get away with!) and my rhythm section won't go crazy weird trying to follow it!
A lot of substitution in real music doesn't involve EVERYONE in the entire band all following the substitutions slavishly. Sadly, an arranger's does... Truth is, in real life, it's often just one or two of you. I personally feel the SMF, if well programmed, gives you MORE playing flexibility than a songstyle.
But that's just me... everybody has a different style!