From my understanding (I did have a BA in this at one time but it's been over 10 years, so, memory's a bit rusty), the "triple tradition" part is the section where scholars believe Matthew and Luke used Mark as a source. The "Double tradition" is the part where Matthew and Luke agree but deviate from Mark, and hence are the imagined "Q" source material. Then there are the sources/traditions known only to Luke or Matthew.
You will notice, however, the orange and red lines indicating instances where Mark and Luke or Mark and Matthew attest, but not with all three. I think those could potentially make your theory unlikely. Because if Q were derivative of Mark, then in theory there shouldn't be anything in Q that wasn't already in Mark. But for there to be some lines that are in Matthew/Mark or Luke/Mark but not in the double tradition would suggest that they had a Q-annotated version of a passage, but opted to drop it in favor of the Mark version. Why would they do that?
I suppose there could have been something like Q derives from Mark but overwrites or omits some details, then Matthew and Luke are written by authors with access to both Mark and Q but are unsure which source has precedence.
This rooted hypothesis would still have Mark be the source of all gospels.
https://en.wikipedia.org/wiki/Synoptic_Gospels#/media/File:R...
From my understanding (I did have a BA in this at one time but it's been over 10 years, so, memory's a bit rusty), the "triple tradition" part is the section where scholars believe Matthew and Luke used Mark as a source. The "Double tradition" is the part where Matthew and Luke agree but deviate from Mark, and hence are the imagined "Q" source material. Then there are the sources/traditions known only to Luke or Matthew.
You will notice, however, the orange and red lines indicating instances where Mark and Luke or Mark and Matthew attest, but not with all three. I think those could potentially make your theory unlikely. Because if Q were derivative of Mark, then in theory there shouldn't be anything in Q that wasn't already in Mark. But for there to be some lines that are in Matthew/Mark or Luke/Mark but not in the double tradition would suggest that they had a Q-annotated version of a passage, but opted to drop it in favor of the Mark version. Why would they do that?