Rather than ask if the switch is a downgrade, why not ask what the differences are sonically and make up your own mind, rather than making it a pissing contest?
Having heard both, they are both fine decks. The 125 will be softer in attack, with less precision and a bit of conceit in the mid bass. You may find this richness addictive as it, roughly, replaces some of the bloom lost in the recording process, or you may find it an intolerable coloration. The treble of the 3009 will be a bit sweeter, or duller, depending on your perspective.
From a historical standpoint, if that matters, the 125 and 3009 are stone classics that will hold their value, or appreciate, in coming years and will probably require more maintenance as well.
If we want to start speaking about used Oracle Delphis, those will be in a completely different price bracket and the appropriate comparison in a vintage Thorens will be the TD-124 MKII.