Solved

Limited team performance

There are no performance limitations for not spending real money other than the obvious ones such as not being able to afford two drivers with legendary ability for 270 tokens each or accelerate your level gains by purchasing double XP.

If your drivers did not use boost throughout the race in an off-line league it suggests you briefly logged in to the race viewer with the account that races in the league. You may have done this before the race began in order to get the Race ID or it may have been a mis-click and you quickly logged out again. It only needs the race viewer to have seen your account logged in for a brief moment and this is enough to de-activate AI boost.

Regarding your race history, you'd need to be a bit more specific about races not counting. There have been a few issues that have caused the numbers not to tally, sometimes it is when the league host asks for a re-run because of server issues but I also believe the numbers have got out of align when certain updates have been rolled out. It's not a big deal, I think almost everyone has been affected somewhere along the line.

Regarding your extra lap(s) in the Mexico race. Go back to the race data sheet, from there you will be able to see on which stint you did the extra lap, how much fuel was remaining as you crossed the line on the lap you expected to pit and how much was remaining when you did actually pit. It will almost inevitably be a fuel load miscalculation.

During a race, the only variable that affects fuel consumption is push level and to a minor extent the use of boost. Tyre wear indirectly influences fuel consumption only because the more the tyres wear the harder you must push to keep temperature in them.

If you use practice lap fuel data to calculate your fuel load you must remember that these laps are completed at constant PL3. If, during the race, you are forced to use low PL to keep tyre temps down (any combination of... high ambient temperature / high speed circuit / soft tyres) then there is a good chance the cars will do a lap more than you anticipated, especially if you added a small safety factor.

You compete in a two car league. With two cars it is possible to score two podium positions in one race. Some managers who compete exclusively in two car leagues may have more podium positions than races they have competed in.