the horse has 10 slots , the camels / turanian rhinos/elephants and T4 bearers have 35 slots of inventory (and weight is not considered on thralls) so yes they are quite the upgrade in terms of space . but depending on witch follower you already have I would say the best to farm a lot is still to respec in full encumberance plus 2nd or 3rd survival perk (since you become the bearer 
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