They did know that paper tube tickets to heathrow and or ealing broadway wouldnt be valid on the elizabeth line
Not then. The Heathrow fares issue was sorted later on (like a couple of months before transfer - and so 2 years after the Elizabeth line branding), with lots of stuff going wrong for TfL to get where we are. Not sure why Ealing Broadway via Paddington NR isn't valid as the line out to West Drayton is integrated into TfL's fare structure on Oyster (and has since the beginning) and I'm getting quotes for cash fares for Ealing Broadway
rail station to Marylebone tube station.
And paper tube tickets are an anachronism - now as well as then. While you can buy them, they are either travelcards (and thus valid on everything within zones 1-6 or 1-9, except for HEx or Javelin services), or specific single tickets that do station to station. That you can't get single paper
tube tickets at Heathrow rail stations is mostly as there wasn't any need for TfL to create such a thing - it's a different thing to not abolishing them as has happened on the network they had pre-2010. TfL don't quote cash fares for the Liverpool Street Overground lines, but do for the ex-Silverlink ones - because the ex-Silverlink ones transferred before Oyster was overwhelmingly dominant to the point where nearly no one bought paper singles.
Plus, while branded like one of the tube family, the purple roundels do say "this is a cousin, not a sibling - it's different". Now that's never, IME, been enough for the people who want a Metro/RER or U-/S-Bahn branding distinction between a line that travels more than a hour out of London from Liverpool Street, in full-sized trains, through central and inner London to beyond the Greater London boundary at half-hourly frequency, and another line that travels more than a hour out of London from Liverpool Street, in full-sized trains, through central and inner London to beyond the Greater London boundary at half-hourly frequency (and note that it's the red-roundel trains to Amersham and Chesham that take longer than the purple-roundel trains to Reading!).
It's like this. They need all the zones from 7 to 15 to cover from Iver to Reading. TfL set the caps for 7, 8 and 9; LNW set the cap for 10; GA set the caps for 11 and 12; GTR set the caps for 13 and 14. It's not possible to co-ordinate all that into a sensible structure acceptable to GWR.
True, unless GWR was like GA or GTR able to accept a long zone covering 6 consecutive stations (OK, Broxbourne-Hertford East inclusive is only 5, as is Mertsham-Hooley inclusive). The issue here is 'acceptable to GWR', rather than 'It's not possible to co-ordinate all that into a sensible structure'.
My point was mainly that it is nonsense that they knew back in 2016 that Oyster wouldn't be valid, especially given they were still talking about zone 15 being reserved for the whole line to Reading internally not very long ago.
As for the issue of trying to get Oyster, surely they could have given Iver and Langley a zone under 10 as only TfL would serve them, with Slough (as a GWR station) given zone 15 (which could extent to TfL-only Burnham and Taplow). OK, that doesn't cover the last three stations, but it deals with the 4 TfL stations, and all but 3 of the stations served by TfL services (which would be ones where people would tend to board GWR services anyway) - it goes a long way to addressing the problem. But they aren't doing that!