If anyone can elaborate, please let me know; they're welcome. 
This is a massive subject, but the huge elephant in the room is that no musician operates in a vacuum.
I am certain that a lot of changes in Pick's playing were as a result of requests (to put it politely) from 'above'.
In a way, everyone in the band is there to serve the songs and as such the songwriter wields a lot of power.
In the beginning bands are more of a democracy, but over time as the importance of certain people becomes more evident, that democracy breaks down. (Look at The Police, example Sting). In it's harshest analysis, Dire Straits would be nothing without Mark's songs and guitar playing. So quite early on he becomes the most powerful member of the band.
Pick has spoken in recent interviews about being asked to play harder and louder. This request came from Mark, but was backed by John. He probably tried to resist at first, but then thought he could accommodate the request and stay in the band.
Playing much harder definitely affects your technique, also the things you choose to play. In the end, Pick decided he had to leave the band, this was for various reasons, but one of them being required by Mark to play drums in a way that he (Pick) didn't want to play.
**So** if you want to discuss the way Pick's drumming changed over a couple of years, it might not just be about Pick, or his personal choices, but changes that were imposed on him.
Thanks for your participation and thoughts, Chris W.
Actually, I'd be interested in an analysis not focused on why he changed his approach. You were very punctual, and you certainly received instructions from above to play louder. Besides the band having a new configuration compared to the original quartet, now with keyboards, I'd be interested in knowing what's really going on with his approach to SOS in 78/79 and 80/81. What's changed? Also, the drum kit seems to have changed—a new tone, a new approach.
In other words, I'd like to know how things worked live on the drums in 78 and 81, taking the song "SOS" as a starting point (he went from approach X to approach Y, from 78 to 81).
I initially chose "SOS" since this song spans Dire Straits' entire trajectory: two tours with Pick, two with Terry, and one with you, Chris. Each era has its own distinct feel and approach.
I'm wanting to look at these songs a bit through the prism of the drums rather than the guitars, starting with SOS.