You will see many different opinions about MT. Puppy farming would stop tomorrow if the demand fell away so the question is how do we do that? For me, that involves working to make people aware of puppy farming, encourage adoption of a rescue rather than buying a pup, and also doing our best to raise the welfare standards for breeding bitches in the hellholes they are currently in.
Wales has its own Government now and Animal Welfare is a devolved responsibility so part of what I do as a volunteer is things like FOI requests to Councils, taking part in cross sectoral groups on different aspects of things like data sharing (sounds dry but is quite important) and of course the recent consultation on changing the puppy farm Regs in Wales - a huge chance to improve matters greatly, working with the anti puppy farming coalition, CARIAD and Puppy Love.
MT did not participate in the recent consultation about the new regs, has not campaigned about microchipping (current consultation in Wales for all dogs to be chipped) does not lobby politicians, does not take part in Animal Welfare Network Wales events, is not a charity (it is a business), does not publish its accounts or adoption figures (sources, numbers rehomed, etc) and does not do any form of campaigning about puppy farming/local Govt inspections, despite being the largest animal rehoming organisation in Wales (it dwarfs even DT and the largest Council, Cardiff) and probably one of the largest in the UK (it rehomes at least 2000 dogs each year). Many people will say, quite rightly, as you have, that MT have helped find new homes for breeding bitches and pups, but without any action on the root of the problem this to me actually becomes part of the problem rather than part of the solution.
If you take the analogy of say the greyhound industry, many charities involved with pointies manage to both rehome ex racers and campaign for better/higher welfare standards - I don't see it as an either/or, but as being complementary and both are essential. Actually, I don't think MT is unique in this respect - overall, I think rescues in general are not brilliant at the political choices/lobbying to make effective changes though are very good (in general!) at taking care of dogs and the short term, immediate side of things. It's very easy to look at a dog on a website and think that by adopting it, you are solving a problem, but often all it is doing is creating a vacancy for some other poor bitch to fill.
Sorry, bit of an essay there, but I think you have hit on a very interesting point about dog rescue work in general and the role of rescue organisations.
In any case, MT and Wales in general could find themselves overtaken by events. It is likely that in the next two to three years, we will be flooded by pups from Central and Eastern Europe. This process has already started and lower regulations, less inspections etc will mean that even high volume puppy farmers will not be able to compete on price. Ordinary purchasers won't see a difference (except a drop in price) since puppy farming is essentiallly a wholesale business anyway. This is going to be a welfare clusterfuck on an epic scale - I am quite depressed about it.