I didn't think about every album and about DS / MK calendar. First DS album was a turning point for sure, but not Communique. Making Movies was another turning point. Another example: The Notting Hillbillies, Golden Heart for sure.
I tend to agree with this, of the six Dire Straits albums I'd argue that four can definitely be considered turning points - the first two you mentioned plus Love Over Gold (the biggest and most obvious change in musical style) and Brothers In Arms (unprecedented commercial success and several big hit songs). I agree that Communique wasn't a turning point, it is fairly similar in sound to the first album but didn't do as well commercially or critically. I'm not sure about On Every Street - it has a better case than Communique, as there is a noticeable country influence creeping in which foreshadows Golden Heart, but it feels more like an evolutionary step than a true turning point. I see Golden Heart as a big turning point not just because it was Mark's first solo album but also because there's a clear change in style with an unprecedented emphasis on love songs and sounds that would have sounded out of place on any Dire Straits album (for example, I think Darling Pretty would have fitted okay musically but the celtic intro and romantic lyrics give it a different feel from the band' style).
There isn't always a correlation between the biggest turning points and the best albums in my opinion, for example I think Sailing To Philadelphia is a stronger album than The Ragpicker's Dream but I definitely think the latter is one of the biggest turning points in his career as there is a significant shift in style from that album onwards - less rock and roll, more folk and blues, fewer long guitar solos, to name some of the more obvious changes. By contrast, Sailing To Philadelphia seems noticeably closer to the Dire Straits sound and feel than Golden Heart, let alone any of his later solo albums - I suppose a 'red herring' rather than a turning point. To use another example in Bob Dylan's discography I think Bringing It All Back Home is probably a more important turning point in the truest sense as his first electric album than either Highway 61 Revisited or Blonde On Blonde, but I would consider those two to be the better albums.
