Only newest build date, as 379s are still just a type of Electrostars and they had been around since 2000, based on the 1990s Turbostar which the East had first for branches, Norwich-Basingstoke and then Cambridge-Norwich. When the West got 379s the East had the more moder modern design 360 Desiros. The 379s while good are a 20 year-old design bought by NXEA to replace 317s which were then considered too old at 20+ year old but are still here now.
That's a rather bizarre argument. Yes the Electrostar is a rather dated design* (I'm impressed you only stopped at turbostar, rather than continuing to trace the lineage back to the networkers), but there are only so many things you can do when it comes to a train, at least from a passenger perspective. The 360 is a notionally newer design, but they are both 4x 20m, doors at thirds, 100mph, air conditioned EMUs - they're not radically different to the passenger (apart from the seating and inter unit gangways) at which point the date they rolled out the factory does become the most relevant factor (though still comparatively irrelevant compared to things like reliability and performance)
*though the 379 was the second of the "gen 2" electrostar which began with the 378 and ended with the 387, a reasonable step up from the existing electrostars