Number of weapons on Space Marine vehicles vs ours

So I have a question about the number of side weapon systems on SM vehicles vs Custodes. Usually beside the main weapon those SM vehicles also have 2-3 side weapon systems (for example the Lancer has 3 other small guns beside it anti-tank cannon, or even Brutalist Dread being a melee-focus unit still has 3 guns) while our banana vehicles only have 1 small weapon aside from the main weapon (Grav tank has a bolt cannon with 3A Rapid Fire 1 or Comtemptor Dread only has a combi bolter aside from a S9 multi-melta). But the point of SM vehicles usually equal or even much lower than ours. Is this because Custodes' vehicles are outdated and need heavy rule update; or we are actually the balance army and SM stuffs are just over-designed?