So you are happy to extend journey times to the south west? Even a 5 minute journey extension is an extension. Would passengers to the north west or north east tolerate such an extension? Oh no, of course not. But they are getting vastly speeded up services, whilst poor old Cornwall still has the same journey times to London it had in HST days. No wonder levelling up is needed, I'm just not convinced the Government are looking at levelling up the right areas of the country!
Whilst I agree that Cornwall doesn't seem to be in the government's sights for vote winning promises, you should be careful of what you wish for. Although misguided impressions of EV ranges are at play here, there will be increased rail travel to Cornwall for holiday purposes, and ignoring HS2*, Crossrail will have a big impact of that decision.
Those travelling from outside Central London, (i.e. almost everybody) will benefit considerably:
from East Anglia, passengers will change at Stratford or Liverpool St.
from the East Midlands, passengers will change at Farringdon
from Kent and Sussex, passengers will change at Farringdon - maybe changing at London Bridge on the way
Currently, all of those are forced to use the north side of the Circle Line, so a qick flip over to Crossrail at OOC will be a lot easier. The LU connection is frequently heavily loaded, with stops at Baker St Junction and trains running on yellows (figuratively speaking).
I might ask, when is the Crossrail/GW part of the station likely to open, will it be before HS2 is open?
* Slightly off topic