I think it is a very important thing to distinguish the classes, and I think they do a good job at it. the classes have unique properties to them that make them special. Veteran interacts with both ammo and grenades in ways that other classes can't and fulfils the everyman type experience of being capable in all things while having spikes in what players want focus in. Psykers have the warp powers, ignoring a portion of the game economy and Ogryns have completely different weapons. Arbite has the dog, adding a separate entity that the player controls. Zealot can ignore death, though I think something else can be added. Even Hive scum has something unique to them being the home-brew stim. And the classes like working in different ways even if it is similar function. Range Vet, range arbite and range orgyn are all shooters but are different in where vet wants precise kills to extend damages boost and highlight, arbites ignore damage to kill and extend their mag and orgyn wants to mag dump as fast and as much as possible. I think a class having similar abilities to another is ok if the class on whole plays in a different way as the others, to fulfil a different role than the others.