Combining the 43 and 143 into one service would result in a messy timetable
The 43 is a clean every 10 mins frequency end to end. The 143 is at different frequencies at different times of day, different days of the week, semester and holidays also being different.
I think it would still work when you take into account that the 143 is also operated by Sharston depot, and buses now run back to the depot for their break, so for negligible difference to resources, you could actually run every 5 minutes from Northenden to Manchester. Then any extras beyond that which are actually needed, could run unadvertised to the public as dupes. Bearing in mind that now with no MagicRider or operator specific tickets, there is no reason why students aren't using any other normal service too like the 41.
But anyway, the core point stands - 142 is just a short working on the 42, 143 a short working on the 43, there's no justification in different numbers, southbound the destination tells you that and northbound it's irrelevant.
The 42 is even more messed up, because there are short 42 which just run Piccadilly to East Didsbury, as well as the 142, and some of these follow eachother. Weekdays from Piccadilly, there is an 18:49 142, and then a minute later at 18:50 there is 42 which terminates at Parrs Wood and they run 1 minute apart from eachother for the entire route. Similarly on Saturdays, 06:39 the 142 leaves Parrs Wood to Piccadilly, then at 06:40 a 42 leaves, starting from Parrs Wood, to Piccadilly. Are there really 140+ passengers wishing to travel on buses leaving Parrs Wood at 06:40? Because I can't see that somehow. Of course the closer you get into Piccadilly, the more other buses you have joining you. It's a complete waste of resources. A fuller 42 timetable to replace the 142, alongside reviewing the 42A/B/C routes to see if there is a way for these routes to operate better by not running through to the Wilmslow Road corridor (unless there is significant demand 'cross' East Didsbury, but there isn't in my experiences.
I also wonder if there is anything we can find out about the travel patterns which could make boosting other routes more attractive, or any links missing perhaps? For example would a 10 minutes 41 be beneficial between Shudehill and West Didsbury and run some extra shorts there rather than so many 142/143s? Gets people to other parts of the city rather than just Picc gardens.