That may be true... I didn't play storm of magic so it entirely possible. But without any expansions and using only the core rules, they are an extremely sub optimal unit. Monster mounts are typically a poor choice because they can be shot out so easily from under your character. In the manticore's case, this is especially problematic since he is so squishy. The best mount options for WoC is either the daemonic mount (for immunity to killing blow) or my favourite the disc of Tzeentch for mobility. In either case, field the unkillable "Hortennse" Chaos Lord/Hero.