Depends on how Hitachi interpreted this line in the Train Technical Specification I suspect:
So the specification drawn up by the DfT clearly had Dawlish in mind but what is "spray" and does what we've seen today (and on the other occasions this has been an issue) count as "spray" or not? Plenty of blame to go around I suspect but at least someone had the thought that best specify something to include provision for salt water exposure I guess.
Why would a politician ever call out the real issues? If they did that then it might raise uncomfortable questions about who specified these trains, who agreed the operational contracts with Agility Trains, who decided on the funding arrangements, etc etc. The answers to those questions could be very embarrassing for those same politicians. Far easier to keep shtum and let GWR take the flak.
Saltwater exposure is partly to blame for the dampener cracks affecting the IET fleet, so I doubt it was that well engineered…
I agree that “spray” probably doesn’t extend to include a huge wave at Dawlish though and I struggle to think of any stock that would appropriately cope in that sort of condition, it’s just that the DfT / Hitachi / Agility shouldn’t have made such audacious claims.