People will no doubt be quick to blame privatisation (even though pretty much all stock was agreed/ordered with DfT consent - or previous iterations of central Government planning/control), but this kind of thing happened under BR - trains are ordered for a thirty/forty year lifespan but generally without much of a plan for long term use (other than the likes of Crossrail, where stock is expected to stay on the line for its natural life).
Are 332s a wasted resource? Now, maybe they look like this. But the prospect of Crossrail was a pipe dream in the 1990s - there was a need for EMUs - it made sense to build new ones with high internal specification to justify the £15 fares. The fact that we've no use for them after "only" half their lives is regrettable but it made sense at the time.
Under any system, the railway is going to be full of short term decisions (e.g. the crowd pleasing order of a hundred and fifty carriages, but split between several short units with no corridor connections, fully diesel powered at a time we are meant to be reducing carbon emissions).
You don't know what future passenger numbers will be - people criticise orders that have been too small/short in hindsight but then who knows what passenger numbers will be after three months of coronavirus? Maybe it won't be long until we are complaining about a TOC that ordered trains that turned out to be too long (once a larger proportion of people get used to working from home on a regular basis).