Sorry but that is nowhere near correct.
On Saturday 29 April (last date I have figures for), at 1:40pm the P&R at Parkway was only 21% full. It has 1,229 spaces. There is also the Station car park, which has another 750 spaces, meaning there are approximately 2,000 spaces just over the road from the stadium. If 21% of the total was used it would still leave nearly 1,600 spaces for football fans. Don't forget, not all of the spaces at The Kassam are available to us either, as a fair few are used by cinema goers and other users of the Ozone facilities, so it really is no different.
Furthermore, at the same time, on the same day, there were a further 1,625 spaces available at Peartree and Seacourt, which were less than 30% occupied, meaning a further 1,150 spaces were empty. The club will be running buses to the stadium from ALL P&R sites around the city and surrounding area, with incentivised tickets available to fans.
If you still want to drive, and park near the exit to the P&R at Parkway, I really don't see that it will be any different at all to your current routine, neither will getting away after the game. Also, part of the plan is to provide enough things for fans to do before and after games, so that fans arrive and depart over a longer period of time, meaning that people like you, who want to rush straight off, will in all probability find it even easier. And all of this ignores the fact that most people WILL NOT be driving anyway.
There really is no more to say!