They do check them. I've seen people stopped and sent to the RPIs when they've been available.
If there's only the people on the barrier available, with the RPIs not being there/not available, what else are they supposed to do? Deal with the person by themselves (if they even can/have been trained to) and let hundreds of people just stroll through unchecked?
I'd suggest that the barrier staff are mainly there to act as a deterrent against blatant and intentional fare evasion, give an impression of security and provide reassurance for the 'I shouldn't have brought a ticket as no one can be bothered to check it...' crowd.
In no way would I describe those platforms as 'done'!
Yep, they're done apparently. And they're already almost as filthy as the old platforms, so you can't be blamed for not noticing the difference. The only difference is now that the platforms get flooded with water every time it rains.
Here's hoping the work upstairs is much more impressive, which, to be fair, it should be.