Well with the recent modification to HS2 the only three significant population areas in central-England without HS2 access are Leicester, Nottingham and Derby.
Total reconstruction of the ECML and MML timetable will be required to deal with the new reality, and if you want to provide fast trains between those destinations and other destinations and between those destinations and London does not necessarily divert everything to Nottingham.
For some reason you are arguing for massive expenditure and cutting services to Market Harborough to improve Nottingham's service - when I can improve Nottinghams service using paths which are surplus to requirements by HS2 if I go by Grantham.
Why should Market Harborough suffer just to allow the MML to retain its historical fast train "turf"?
MML has four trains per hour to Leicester at present. That could easily increase to six in future to be comparable with, say, the ECML service to Peterborough, which is the sort of service Leicester deserves as it doesn't benefit from HS2. The bulk of any expenditure, probably not much beyond the electrification already committed, will be to support this.
With this many coming into Leicester I see no problem in continuing them as, for example, two Nottingham fasts, one fast and one semi-fast to Derby and possibly beyond, and two semi-fasts to Toton providing northward connections from intermediate MML stations. Capacity is much less constrained on the four-track north of Leicester, especially once this is restored south of Syston as is proposed as a freight enhancement. Turning more back at Leicester instead would probably involve extra spend on more platform capacity there.
A fast Nottingham train via Peterborough is an entirely new service only really serving London and Nottingham, since anywhere in between probably has all the service it needs to both places.
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What modifications? If you are referring to the changes to the location of the Sheffield station, I wasn't aware that this also involved the axing of the HS2 station at Toton?
Toton will provide fast links (while not direct to the city centres) north to Leeds, West Yorkshire, York and the North East for Nottingham, Derby and Leicester, and faster links south to London, Birmingham and the West Midlands from Nottingham and Derby. So I'm not exactly sure what you are trying to say in that the "three significant population areas in central-England without HS2 access are Leicester, Nottingham and Derby".
While it has its benefits and the geography makes it difficult to see how a better solution could have been found, Toton is far from ideal for city centre access.
The time from London is about 53min and the tram into Nottingham would take somewhere around 30min with around 17 stops. The few fast Nottingham Meridian trains today are only just over 90min. With electric operation plus the transfer of Parkway and Market Harborough stops to other services as I suggested above, this could be equalled or slightly bettered at least every hour. So it is likely that HS2 plus tram, while good for the western suburbs, would be no quicker and a lot more hassle than the existing rail route for centre-to-centre journeys. A connecting train service via Beeston might be 10min or so quicker, but only if the station layout and the timetable allow really slick connections. With all the other regional links using the same infrastructure - not least the Nottingham and Derby connecting trains probably having to share the same tracks from Toton - this will be very difficult to achieve satisfactorily.
The same applies to a large degree to Derby, except that it doesn't have the tram and probably never will - Nottingham to Toton is almost continuously built up but Derby to Toton is mostly rural so a service with low top speeds and frequent stops isn't appropriate.
In both cases I contend that good access to city centres is essential to the success of rail. An out-of-town station allow the local affluent population to drive there and travel to London, whereas strong links to centres encourage inward visitors by train and tends to spread prosperity to the cities of the Midlands and North. HS2 doesn't and probably can't deliver this for Nottingham and Derby so it is important to maintain good links via classic rail.