I'd suggest going back to the roots and reading up on European wild rabbit behaviour (not Cottontails which are different). I think you'll find in quite a lot of ways both sides are right
The Private Life of Rabbits is a good one.
Rabbits don't live in one big happy colony, they live in small family groups within that colony and there is territorial behaviour between those groups - mainly during breeding season.
However, how they display that territorial behaviour and determine hierarchy is important for understanding why bonding pet rabbits can be troublesome. For example, a rabbit's way of saying 'I acknowledge you are the boss and don't want to challenge you' is moving away from the boss. Put rabbits in a confined space and there is no way to move away and give that signal. Instead he's stuck in the other rabbits personal space i.e. signalling he wants to challenge which increases the risk of fighting.
Another example... you have a single rabbit that's been on it's own, so he's always been top dog. Best food, best sleeping spots - all his. Now add another rabbit that feels exactly the same way. Two rabbits that have always been top, never been challenged and have no social experience - again the environment increases the fight risk.
Female rabbits - they interact together in the fields, but have their own individual burrows for nesting. Unneutered pets have the same nesting drive. Which is why female rabbits often display hutch aggression - the hutch is their nest which only belongs to them. Put two together in a hutch, add in no experience of living in a social group and you can have issues even though multiple females in the wild can be in the same social group.
Wild behaviour explains a lot of way bonding can be hard - you're trying to mix two 'groups' from different territories, but rabbits that are bonded are often very happy (they belong to the same family group) and groom/rest/eat etc. together.