The problem with space marine hover tanks is it dilutes the imagery of both them and the other factions.
Instead of strong archetypes, it becomes more of a mush where everything is the same generic tacticool guy.
how does space marine hover tanks dilute the image of them?
Its not just Space Marines that he's talking about. It's the relationship between Space Marines and other factions. The Imperium has been limited primarily to ground vehicles for a long time. Sure, the Land Speeder exists but it was supposed to be that rare exception. Imo
the iconic SM
tank is the Land Raider. Rhino, too, although it's not really a tank.
On the flipside, other races have some flying vehicles. It sets them apart and signifies a different level of technology and a less restricted philosophy regarding science. But maybe more important than that, it's different! Different factions get different stuff. Now that Space Marines have a large flying tank, it detracts from the exclusivity of the tech, and chips away at faction differences.