As a daily user from the outer end of the Reading line I couldn’t give a stuff about loading better or whatever other “benefits” SWR try to sell. I’m after a comfortable seat and a seat back table - both of which the 458s have and the Aventras seemingly won’t.
I think it needs to be acepted that there is a greater need for people to actually be able to get on, throughout the line. Admittedly you said you get on early but the 458s have few seat back tables anyway since they're mostly bays of 4. These will be a big help for the majority of commuters similar to people complaining about 700s and ignoring the fact that they couldn't actually board before they came about. Reading has been 'downgraded' to metro/suburban that's just the way it is.