I quite agree. I have regularly traveled on 455 and 450 over the years and the 455 stock is faster at opening. No question about it. The doors that open faster are on stock being phased out and where they wish to replace the guard during disruption.It has everything to do with the slow opening doors on a desiro, the guard has to open a local door to look out down the train before they can release the rest of the doors, if that door takes 5 seconds to open then there’s nothing the guard can do to speed up that process short of not doing the required safety check.
The doors that take longer to open are on stock not being phased out and thus where they wish to only run them with a guard during disruption.
I know there are other reasons for getting rid of the 455 stock.