There you go, I've corrected your post for you
1. The old bay platforms at Blackfriars were on the wrong side of the station for the proposed increase in services and would have meant a lot of conflicting moves hence why we now have the bay platforms on the west side in order to reduce the number of conflicting moves.
2. It was proposed to terminate the Wimbledon services in these bay platforms at Blackfriars which would have made the mainline services more reliable however due to opposition from the locals and the local MP, that got cancelled.
3. I don't know if you are aware or not but HS1 goes to St Pancras and not Waterloo for a number of reasons not only to free up platform space at Waterloo which is finally happening but also to speed up Eurostar from the very slow pace though South London to Waterloo to being a attractive form of travel between UK and Europe.
4. As it's been pointed out time and time before, they never built a 4 platform station at
St Pancras due to physical constraints so regardless even if Eurostar didn't use these platforms at St Pancras, someone else would have done be it South Eastern High Speed or East Midlands Trains.
5. That's your view and a tad upfair to these who have struggled to make the timetable work both in the past and now.
6. Thameslink services don't all start or terminate in Brighton no matter how bias you believe yourself to be, they start or terminate in Bedford, Brighton, St Albans, Luton, Sutton/Wimbledon, Sevenoaks and that's before the newer destinations that the current timetable brought in by GTR.
7. For Brighton line passengers, again you seem to not be aware the line has bi-directional signalling so unless its a total blockade, services can still run using the bi-di signalling:
- Balcombe Tunnel junction to Copyhold Junction (just north of Haywards Heath).
- Haywards Heath to Keymer Junction (just south of Wivelsfield).
- Keymer Junction to Preston Park.
You also seem to have forgotten that the section from Wivelsfield to Preston Park can be bypassed via Lewes at Keymer Junction rejoining the main line at Montpelier Junction.