I think the ferries have been cheaper for quite a long time… possibly always.
The tunnel is just better for us… quicker departure, quicker journey and just less faff. The tunnel journey is over and you are on the French autoroute in the same amount of time you’d only just have boarded the ferry, with a 90 minute crossing still to go!
A baby adds another dimension too. Taking a baby on the ferry is a mission, whereas the tunnel is easy, just leave him in the car seat, or take him out and play with him in the van for the 30 minutes it takes, then back in the seat and go.