The Elizabeth Line largely replaced 387s on the stoppers, but those 387s still operate semi-fast services calling Slough/Maidenhead/Twyford, so for those commuting straight into London there are options available to change onto faster, better equipped services.The Class 165 and 166 which ran the Paddington suburban services until electrification and then subsequent replacement by Elizabeth Line services have toilets.
The Elizabeth Line again isn’t a great comparison, few would argue that it’s anything other than a glorified tube train for most of its length, and as above the Paddington - Reading stretch runs parallel to other options for those going end to end.