Those are only the formats for a "speedy" tournament.
You can of course opt for a slower format. More of a league system, with 1 game per month. Here i'ld again aim at 4 team round robin
Again the example of 25 teams. => 4 groups of 4, 3 groups of 3
After 3 months, seasons is ended. First seasons would have no single winner though. 7 winners + best placed go to highest divions.
Month 4 = entries for new seasons
Month 5 = start of season 2. let's say all 21 teams stayed = 4 left and 9 more joined => 30 teams total
Highest division => 8 teams, 2 groups with 4 teams => 2 groupwinners play an extra game for the titel. teams 3&4 relegate to division 2
2d division => 16 teams, 4 groups of 4 teams => groupwinners advance to division 1. nr 4 relegates to division 3
3d division => 6 teams, 2 groups of 3 teams => top 4 teams advance to division 2
and so on
Other option for the "slow" format
the standard leagues + playoffs = very long. About 1 "season" per year
