Firstly, I never said the line would serve Durham, you're strawmanning me. The line very specifically would not serve Durham, it would probably head northwest, bisecting Durham & Chester le Street, and end up using the (now abandoned, but extant) eastern approach to Newcastle Central north of the Tyne.
I also have never said trains would serve Tees Valley Parkway (Durham Tees Valley airport is so called because it is in county Durham, not Durham itself, as I have said before, it's equidistant between Middlesbrough and Darlington) and Darlington Bank Top, I have said HS services would serve Tees Valley Parkway only, and all conventional services that currently serve DBT would still serve it. This is a pretty horrific argument John, given you're effectively saying 'If you did it this way, it would be bad'. But I'm not arguing to do it 'that way', I'm arguing to do it the way I've written it down.
Unless further clarification is needed, HS2 would be completely separate between Cross Gates (Leeds, where it leaves the ELL) & Newcaslte Central station. Tees Valley would have split-level interchange between the Tees Valley Metro & HS2, the line would not serve DBT or Durham, or use the ECML to get into Newcastle.
As for using DBT on it's own, that's great for Darlington, it's bugger all use for Teeside. which is why DTV is the best site for TVP. As for platforms being moved, bingo! Yes, this is quite clearly what I've said. the airport station is being moved closer to the terminal anyway, but I'd just assumed a very short tunnel under the runway & a station in a cutting with escalator/traveltor interchange.
As for Teeside not being particularly wealthy, yes. By bringing it onto the HS2 network you make the region as a whole more accessible, you create jobs, and you free up space on the classic lines for direct Middlesbrough-London services on a clockface timetable. Much better than the status quo. As for the good people of Guisborough, well, they might not use it to go south, but going North (To Newcastle) it would be of huge benefit, and would give Teeside the benefit it needs in fully integrating it into the northeast, which, because it's quite far away from Tyne & Wear (in a local sense), it currently isn't.
The line north of Leeds would firstly serve Newcastle as well, so at least 3tph there, plus a much quicker service to Scotland (90 minutes as opposed to 3.5 hours) would justify an increase in frequency. I don't imagine capacity would be used up straight away, but it would certainly go up after the line was built. Leeds-Newcastle in 30 mins, Sheffield-Newcastle in 50 mins and Nottingham-Newcastle in 80 mins would also create new journey markets which currently don't exist up the east coast.
As for the city centre station site, no. An exit on the corner of Meadow Lane & Waterlo street would be perfectly positioned for a pedestrian boulevard across Meadow Lane, and a new footbridge across the Aire, leading to a new southeastern City station entrance in the area bounded by Sovereign Street. A 2 minute walk maximum, Leeds City & Leeds Waterloo (HS) would be separate stations, but they'd be easily accessible from one to the other (rather like Wigan Wallgate & Wigan North Western). Yes, this would require slow speeds, but so does any station, and the benefits of city centre stations (see France) are much greater than those that are Parkways. So while there'd be a timeloss, the journey would be quicker, compensating for all those people who'd have to spend extra time on a slow train getting to your proposed parkway.
This is summed up nicely in your last paragraph, where 'getting York' for a time saving trades off the loss of the 3rd biggest city in the country. I'll say it again, York is 1/6th the size of Leeds, has about 20% the business population, and is mainly a tourist destination. Go to York station on a morning (or in fact any time of day) and see the sardine-tin trains heading into Leeds. Leeds is the major economic centre of Yorkshire, and it makes far more sense to serve Leeds than to serve York, especially given that you'd lose time to stop at York, so the overall time loss of stopping at Leeds (compared to stopping elsewhere) is pointless. Because really John, HS2 needs to stop where the people are. Because that's how railways get passengers. And while a faster connection to London would be good, a faster connection to Scotland would, to my mind, be much more beneficial.