It's not difficult to win the "offline" events in A-spec and B-spec. Some of the Specials/License Tests are move difficult. Just use a slightly powerful car will do.
Some few harder ones are those using same spec cars, such as the Historic racing, Expert level FGT Grand Prix (for b-spec, you need a high level 30+ and experience in braking (for late braking overtaking), accuracy (else bang wall or run out of course) and hot-tempered (aggressive)). Cornering is lowest priority, since just slower cornering.

For endurance, using FGT/X2010 is an overkill and sure-win. B-spec endurance, tune down FGT to 750pp, guarantee win, even use Level 0 driver (straight jump to more than level 25/30+ with one race  ). High level, but very lacking on experience. No need push the driver, just let it be.

Yes, I finished all events in a-spec (beginner, novice, ... , expert, endurance) = 1x Level 24 ticket
Do the same for b-spec = another 1x level 24 ticket

But ... I can share, you will need a lot of time. e.g. a-spec FGT championship 6 races = minimum 4 hours, each race about 30-45 minutes. If b-spec FGT, prepare 6-8 hours, more laps.
Therefore, if you want Cr & Xp, better to grind through Seasonal Online. For me, I just want to finish the game, I don't have the skill, but I can allocate some time.

Endurance, the first 4 races takes about 2-3 hours each.
Suzuka about 5-7 hours, depends rain or not.
Nurb = 4
Tsukuba = 9 (I use the same Mazda)
Sarthe = 24 (FGT without headlights - very difficult at night, but long-straight road winner)
Nurb = 24 (IINM, is R8 LMS and the car retired with exact mileage of it - keep for personal reason)

b-spec endurance is easy, just leave it running and you go sleep or do own stuff.
a-spec need to plan for holiday, 3 continuous days minimum (in my case), with no inside/outside life interruption  . Cause each day will race about 7-10 hours only, with break, tapao/delivery meals, bath in between, that will eat up couple of hours.