It's easily the least complicated and most fluid.
Yes I agree. However... I think it could be more exciting if we had demotions and promotions to and from divisions, at least for part of the season.
Here's 2 different ways I've thought of that we can go about it this division thing.
Full-time Division placements (4 demotion/promotion events throughout the season) (weekly qualifier aside, I like this)
Atfer the divisions have been decided (i.e. from the qualifier), every 2 races there will be a number (3, 4?) of drivers demoted into D2, and the same number of drivers promoted into D1. To determine who is going to be demoted, the drivers' points haul from the first 2 races are calculated and the lowest 3/4 scorers in D1 are demoted, the highest 3/4 scorers in D2 are promoted.
About planned absences: If a D1 driver who finished 3rd in the first race and missed the second race, it would be unfair to demote him because he would be locked into D2 for 2 races. This is why we can assume he would also finish well in the second race. Here we can say 1 of 2 things.
1. He could finish 3rd in the 2nd race too and saying he scored 36 points in each race = 72 points.
2. He could finish have finished 'in and around' 3rd place and you reduce his points a bit, giving him a penalty of missing the race for example and giving him a larger chance of being demoted. He scored 36 points in the first race, and 36*0.75 points in the second race = 36+27 = 63 points. That 0.75 could be reduced to say, 0.5, it's just a suggestion.
Weekly Qualifier placements with 2 demotion/promotion events
Weekly qualifier decides divisions for race 1, 2 and 3. The points haul from each driver throughout these 3 rounds decides Division 1 and Division 2 for race 4. Top 14 points scorers will be in D1, bottom 14 in D2.
Of course though, like the other method it would be unfair if most drivers raced in all 3 and a few had missed a race. We can times their points scored by a certain factor again. If a driver had scored in 2 rounds and missed 1, multiplying by 1.5 would give a reasonable points score of what they could have achieved if they hadn't missed a race. So again we can penalise them a bit by multiplying their points by 1.25 or something.
So by the end of race 3 we will have divisions for race 4 decided. The divisions for race 5 is decided by the race results of race 4. Top 3/4 D2 drivers get promoted into D1, bottom 3/4 D1 drivers get demoted into D2.
The cycle happens again for races 5-7, and 8 and 9. Points haul from races 5-7 decides the divisions for race 8, and the results from race 8 decides the divisions for race 9. That leaves the final race, race 10 to be decided by a classic weekly qualifier.
You might say it's unfair if a driver misses 2 races out of the 3 'points haul' races, but should a driver really miss 2 out of 3 races in a 10 race championship?
Just a few ideas anyway...