They're not wimpy, they're just lovers, not fighters!
Agree with others. Remove any bullies from the herd or keep yours elsewhere with a more easygoing herd. Make sure there's enough room for him to get out of other's way, especially at feeding time.
But esp if the herd isn't secure, there will always be some bickering, until pecking order is established. If there are always horses coming & going, there may always be bickering. Also, not sure just how 'wimpy' your boy is, if he stays to put up with the treatment, even with a fence in between him & others