I would get rid of the fussy countryside branches above Harrow on the Met and hand them over to Chiltern or maybe buses.,
180,000 people live within 3 km (straight line) of North Harrow station, 140,000 within 3 km of Pinner, 90,000 for Northwood Hills, 60,000 for Northwood, 55,000 for Moor Park, 50,000 for Croxley, 90,000 for Watford, 33,000 for Rickmansworth, 20,000 each for Chorleywood and Chalfont and Latimer, 30,000 for Chesham and 25,000 for Amersham. (By comparison, for Epping it's 16,000, 20,000 for Theydon Bois, 40,000 for Debden, 50,000 for Loughton and 80,000 for Buckhurst Hill, but somehow leaving the eastern Central line as the Hainault loop never seems to come up, just cutting the Met - to call it a solution in search of a problem would be charitable.) Of course a lot of people are within 3 km of more than one of those, but there's also lots of people who drive from e.g. Hemel Hempstead to northern tube stations for cheaper fares / more convenient City access.
As for giving it to Chiltern, why on Earth would you move a set of completely electrified routes with eight trains per hour in the off-peak to an operator with no electric trains and which has cut direct London - Aylesbury trains from three per hour pre-pandemic to one in some hours? There's not enough capacity at Marylebone to absorb much more - and if there was I think Beaconsfield and High Wycombe would be the priority - so would Chiltern start serving Baker Street for the sake of it? Would Aylesbury, from whence it already takes twice as long to get to London as from Milton Keynes twenty kilometres further away, have to absorb passengers from five more stations with a less frequent service? Would Chesham and Watford lose services to central London entirely?
All of that's without considering that Baker Street to Aldgate is busy enough that it needs a very frequent service; would you just leave that section with four fewer trains per hour, or find somewhere else to terminate them?