On these aircraft there is no 1DEF. The front row on that side is 2DEF.
I suspect what happened is that the aircraft changed from the config with the front divider and a full row 1. This can happen right up until the day of departure on Gatwick flights.
FWIW I’ve been downgraded to economy in the same circumstance. But I agree these seats have some drawbacks and I much prefer the other config.