Although the Elizabeth Line platforms are higher than standard and the Class 345s have a floor height to match, this height is roughly the same as most existing rolling stock.I can't see how that was ever going to be achievable. There is, still, no standardisation of floor height and thus raising or lowering a platform for one class of train may make matters worse for another.
Isn't this what has happened at Ealing Broadway, that Crossrail trains have a floor height suited to the core stations, which are the same height as those built for HEx, and higher than is typical on GWR, which still runs trains with a different floor height. (Not sure of the detail)
Elsewhere, low floor 755s have to share platforms with EMR 158s at Ely and Thameslink 700s at Cambridge.
The problem with Ealing Broadway is that it has platforms even lower than the standard so there is a larger gap than normal. This gap was there before with previous rolling stock but the Elizabeth Line has given an expectation that things would be better.
The craziest part is that Ealing Broadway was refurbished before those trains started calling and the opportunity was there to bring it up to standard.