If you built Platforms 14-15 at Piccadilly, there would be no point 4-tracking between there and Deansgate. Everything along that route travels at the same speed, fairly slowly because the stations are so close together, and in that situation a decently signalled 2-track railway can easily cope with more than the kind of frequencies you'd want to run on that corridor. The issue is at Piccadilly station because of dwell times. And maybe a question mark over Oxford Road, where we'd hope that with the planned platform lengthening, 2 platforms would be sufficient for the non-terminating trains. Deansgate does have variable speeds because not all trains stop there, but you could solve that by just stopping everything at Deansgate.