Pay History accounts for 35% of a FICO score which means 297.5 credit scoring points. It is the largest category of influence but not nearly to the level that most consumers expect.
The important factor with pay history is: TIME
The most recent activity has the most impact on the credit score. For example, a late payment in February or a new collection account in February or a perfect pay history in February will have much more impact on your score than 1 year ago or even January. The score impact will reduce over time. After about 24 months since a "late" or "perfect" pay history...the score is barely impacted at all.
Keep in mind that even though a 4 year old collection is having very little if any impact on your credit score.....it does remain (as do all accounts) on your credit report for 7 years.
Pay history is important......The most important pay history is that which has occurred in the last 12 months.....Pay history impact is reduced over time.