Quite agree. Trams should be compared with buses not trains. If you do that trams usually come out ahead.
Though i have never grasped the advantages of trams over trolley buses. A modern incarnation of the trolley bus with batteries to give it even two mile range could be much more flexible in routing (yes I know that metrolink trams are flexible
I have mentioned the trolleybuses in Bradford that i rode occasionally as a kid. Excellent and clean, and able to cope with the gradients in Bradford.* Why ever did they scrap them?
*I bet a modern trolleybus could regenerate much braking energy back into the overhead. Doubt the old ones I rode did!
A trolleybus can generally be no bigger than a motor bus because of the need for it to be manageable on the road without guidance. That means that driver costs, the main part of operating costs, are no cheaper with a trolleybus and where numbers are big enough to justify a large tram, providing the same services with trolleybuses means more drivers and more congestion. There are also extra costs for the overhead line, which needs two wires so is more visually obtrusive than for a tram. Bombardier and Lohr came up with rail-guided trolleybuses which could be as large as trams, but turned out to use about 50% more energy due to the poor efficiency of rubber tyres. So at high passenger numbers the economics favour trams.
At lower passenger numbers motor buses are a competitor, with the same driver costs and no need for overhead wires. Batteries give the trolleybus some competitive advantage, but in time are likely also to allow diesel buses to be replaced by more environmentally-friendly alternatives and thereby eliminate one of the advantages of the trolleybus.
So the trolleybus is a niche product and that niche is so small as to be non-existent in many places. The sorts of places where they might be favoured are likely to be very hilly cities (rubber tyres are better for gradients) and those with particular pollution problems.
On the original question, it's very much a case of horses for courses. All the current tram designs in the UK are designed for fairly short journeys, of a similar time duration to a typical bus journey although the tram is probably faster on a segregated track so can cover a greater distance in that time. Tram-trains in places like Karlsruhe can cover routes of about 120km, though typically the city is in the middle so few people will be on board for longer than an hour. These vehicles typically have high-floor centre sections with more comfortable seating for longer distances, leaving the lower-floor areas round the entrances for short-distance passengers as well as those who can't manage steps. I imagine if TfGM or some other authority goes for tram-trains in a big way then they will do something similar with the interiors.
As mentioned, Altrincham and Rochdale do have heavy rail alternatives which are quicker but less frequent, though Altrincham's services is set to double at some point. There have been discussions elsewhere on the forum about serving Bury via Heywood. With hindsight it's a shame that another of the several railways serving Oldham didn't survive - a loop from Ashton re-joining at Greenfield could have given that town easy access to Yorkshire as well as a fast Manchester service. But unfortunately most of that closed before Beeching when the railway geography of the area still seemed stuck in the pre-grouping era.
I've done the scenic route around the streets of Oldham, and its quite time consuming, compared to the previous run through the tunnels.
For passengers to/from Oldham itself this is a benefit, and those closer to Rochdale wanting central Manchester can interchange at Rochdale station. So only a fairly small number of journeys are penalised.
Just because the Bury route had a self contained system of electrification, there would have been nothing stopping a train operator running a service through Victoria towards Liverpool for example, even if it wasn't an electric.
Historically there were steam services between Manchester and Bury too, most of which I believe went via Clifton and joined the current route at Radcliffe. I think the frequency of the electric service at its most popular made it impossible to run a non-stop service by that route more than a couple of minutes faster.