No Professional player that plays over/with SMF's will ever "just play a melody line"...The melody is usually "sung"...The proper way to use SMF's is to remove the parts you want to play "live" ..they could be a counter line, embellished chords, brass parts, organ parts ..or riffs..even bass lines...

It takes more talent to play with Smf's than chording a left hand and a simple melody on the right hand...I can see most folks do not have a clue to playing professionally with sequences...

As for "Pros" that play arranger keyboard...we apparently are the smart ones...Maybe "purist" should learn the benefits of arranger keyboards....they are not only for "auto play"...They are designed for fast set ups and will accept great players abilities..as any workstation available...