It is a massive downgrade in terms of what access to rail services are like in London. I am very supportive of measures to increase local services in London (especially when one considers that London is set to remain as the unicentre of the UK economy), but closing 6 local stations just severely undermines that entire philosophy and will extend journey times considerably.
And I think it bares little relevance that the Catford loop is in 'close proximity' (even that is to be debated; but let's pretend it's true for now

because it's already been shown that trains via Catford form the busiest services in the peaks despite all of these options they seem to have. it's clear that the destinations offered by the Hayes line are not attractive to users of the Catford Loop.
despite being pathetically close to Catford Bridge, Catford is still the busiest station on the route ( It's also important to note that Catford Bridge is the most used station on the Hayes Line as well.) I'm sure you've ever had the displeasure of using some of the services on either of these routes during peak hours but they are very busy and pretty much already at capacity.
Also, I think you've fatally forgotten about Kent bound flows. Let's agree for a second that the users of Catford loop wouldn't be getting a raw deal since they're in proximity of the Hayes line - how on earth do they get to Bromley and Kent etc?
Also, I think you'd genuinely need to quad track the Catford loop or increase capacity on the Atlantic lines for your plan anyway? I'm not convinced that the current peak services from Vic and Blackfriars can be reliably pathed through Catford whilst accomodating Vic-Dart and London Overground (which are already set to get service uplifts)
Between 1645 and 1745, these are 14 unaffected services from Victoria and Blackfriars currently that would need to be weaved through the Catford Loop and Atlantic lines. Is this possible? Or would it need more infrastructure upgrades? if so what?