1x top 10 season (10+ wins) - 10-3, 11-1 (More)
2 top 25 seasons (8-9 wins) - 9-4, 8-5 (Same)
4 unranked but solid teams (6-8 wins) - 7-6, 7-6 (less)
2 mediocre years (4-5 wins) - 5-7 (less)
1 awful season (4 wins or less) - 4-9 (same)
This is in 8 seasons. Go 5-7 and 7-5 the next two years (Both very reasonable), and the 10 year span is the exact situation the OP expects for BYU.