I'm not sure that is the reason. On the rare occasion when I've used that service it's not waited at Oxford Rd and arrived at Piccadilly a few minutes before it's timetabled arrival time. The Deansgate to Oxford Rd section is also one track in each direction so normally whichever train goes through Deansgate first arrives at Piccadilly first and vice versa.

The Manchester to Chester/North Wales service does not seem to be coordianted with the TP Express services from Manchester Airport to Preston and beyond. Two trains are timetabled to arrive at Piccadilly at 07:54: an Arriva Trains Wales service from Chester via Warrington and a TP Express service from Blackpool. As both would require the same platform at Piccadilly it is likely that the Arriva Trains Wales service would arrive at Piccadilly first, but if it's late at Oxford Rd then it may be made to wait as a consequence.

Also there is no apparant reason why the 07:27 train from Chester to Manchester via Warrington would take 9 minutes between Oxford Rd and Piccadilly, other than to meet puctunality targets.

The fact that this is the 07:27 train makes me guess that because it arrives into Manchester at just before 08:00 rush means that it is likely to be a busy service and needs extra time at Oxford Road to offload all of those commuters. Plus from what it seems it is allowing the 07:52 TPX to overtake at Oxford Road. What I have previously seen on these operations are that the TPX airport services use ther track opposite to the ATW one, so as this is on a service to the airport and needs to be on time, it overtakes the ATW on route to Piccadilly.

But that one is a bit of an anomaly anyway since the majority of TPX diagrams on that servce arrive just before xx:59. So Arriva passengers could leave the xx:54 and wait 5 mins on the same platform for an airport connection.