You seem to be saying that you think moving will bring Dundee success, but at the same time you don't want it to happen and you think Saints shouldn't have moved?
Moving rather than upgrading gave Saints far more land/space to expand and improve their facilities. If Dundee only upgrade Dens instead of moving, what conference facilities will they have, what training space, what car parking space? By moving, Saints gave themselves all of those things that have helped the club to make money and grow. An upgraded Muirton Park would never have been on a par with what McDiarmid has given us (and upgrading Muirton was never an option anyway - where would the money have come from?).
Both Dundee clubs should have got their heads together 25-30 years ago and sorted out having one good stadium for both clubs to use. They can't play at home at the same time anyway, so why not just play at the same place? Sell both grounds, combine the money and build one good stadium for both to use. Instead, they've both chucked endless money down the drain chasing after short-term gains, while Saints have flourished in a far smaller city with a smaller fanbase.