The original bit of Metrolink was done very much on the cheap. Even the number of trams was inadequate, the trams themselves were shit quality and much of the permanent way needed relaying. But it was Thatcher-time and it was a miracle anything was built at all.
As I never tire of reminding people, the choice was not between Metrolink and something better. It was between Metrolink and nowt.
The Oldham/Rochdale line, for example. It was falling apart at the seams and major investment was needed if it was not to close. Some people say the trains were better, but new/improved trains were not on offer. It was Metrolink or closure on the grounds of decrepitude.
Metrolink eliminated what was previously a huge revenue subsidy. That's all that made it feasible, albeit on the basis of higher fares and (arguably) poorer quality carriages.
If the day ever dawns when the people of the UK are happy to pay higher taxes in exchange for a really excellent public transport system, we may see an upgrade. But I for one do not expect to live to see that day dawn.