I can confirm this technique when it comes to the rivalry trophies.
I played as Pourchaire in Kick Sauber, 30 difficulty, 10 race season, 5 laps per race, 1 shot qualifying.
I would occasionally drive the practice sessions, most of the time I did the simulated practice sessions.
I rarely chose the specialist tasks or primary specialist role.
I was able to earn all of the rivalry trophies, the level 3 specialist, & the 90+ focus within 15 races.. 1 1/2 seasons of the shortened career mode. Pourchaire ended up at 82 or 83 overall, with 99 focus after 15 races.
The best way to earn focus is to be in a very low level team and just obliterate the competition, while not upgrading the R&D enough to bring the team out of the bottom of the rankings. 1,500-1900 focus xp at basically every race will lead to a lot of focus very quickly.
Using this type of format (short races, one shot, simulating practices.. and not worrying about the championship rivalry) is probably the way to go when attempting the climb to 99 overall.. the objectives appeared to be basically the same as the created driver.. especially the overall totals
Regarding the above question about how to get the championship rivalry to heat up:
After the first 2 or 3 races of the shortened career, a rivalry between Pourchaire and Verstappen appeared. For every succeeding race, I tried to flip the championship ranking of the drivers back and forth. In one race, Verstappen would take the overall lead.. the following race had Pourchaire take the overall lead.
I followed this even when the ai took grid penalties or had very slow starts. When it was my time to lose, I made sure that the points total would give Verstappen a narrow lead. When it was my time to go up, I made sure that my points total remained close (no more than 5-10 points) until the rivalry reached the necessary level for the trophy pop. The rivalry reached the 2nd tier by the end of the first season and concluded by race 5 out of 10 in season 2.