Inquisitiv,
Firstly I should state that I'm not a pilot but was in civilian Flight Test for close to twenty five years. The route you mapped out is probably the only one I've seen that can lead to a TP position but, as you say, it's a very slim chance to succeed that way. If you've done the research, you should also have realised that for every TP there are many more members of the test team, all of whom must do their job correctly to complete the required testing and achieve the certification of an aircraft. It can be a very satisfying experience to be part of the team even if you're not sitting up front.
Bear in mind that, even if by some miracle, you could follow the military path, you're up against a one in thousand or more chance to get an entry to ETPS, AX, Pax River or Edwards. I've been privileged to work with some of these (some graduates of more than one) and they are both exceptional pilots and analytical engineers.