A player at 1800 is likely stuck there because his heroes have just reached 5* +2 but do not have suitable equipment yet to raise their stats further (wrong suffix, no/little set bonuses, etc).
A player at 2400 is likely has proper equipment but do not have the squad synergy (i.e squads that aren't well thought out) to deal enough damage output or survive.
A player at 3200 is likely to have proper equipment and team synergy, but may be lacking in talent points, and/or wasting orbs to overflow.
A player at 3600 is likely to have a nice squad with a considerable amount of talent points, but is unable to counter the trigger ranger meta that plagues 3600-4200 (not using Guan Yu, ZhuGeLiang, CassMB, and other units to counter trigger rangers).
A player at 4200 is likely to have beaten the ranger meta at 3600-4000 (or is running a ranger squad himself with RheaGoon or Guan Yu to counter attack), and is now unable to beat the cassandra/rhea/gy meta at 4200-4600.
A player at 4600 is in the top 30 of the server.