And 300W will give you 4mph, requiring a mere 50W contribution from the rider to a 250W limit. 250W will still give you over 3mph - walking speed. And remember that the 250W value is continuous rated power, not peak.
Now consider how incredibly rare 20% hills are. I don't mean hills that cyclists say are 20% but which are really 15% - there are hundreds and hundreds of those. Actual 20% stretches are short and infrequent.
250W is enough assist for anyone who wants to undertake any normal cycling in the UK. If you want a bike that puts you on a par with trained cyclists, without you having to put in any effort at all then what you want is an electric moped, not an EAPC.
Maybe a visit to North York moors may sway your view somewhat.