Yes, you must have some trust in the ledger owner

Then I fail to see the advantage of a decentralised system, as we can let the ledger owner sign each transaction, instead of a consensus.

although, as mentioned in another post, depending on the type of asset it may not be such as issue.

Can you elaborate or point me to that comment?

Also, we think there is a benefit to payments not being centralised, even while issuance is. For a start, the ledger is signed by multiple parties which increases trust

I would consider the ledger owner’s signature more trustworthy than multiple third party signatures.

and resilience against faults (malicious or not).

Making it decentralised has a much larger attack (and bug) vector, so I wouldn’t conclude that decentralised in itself is an advantage (which I think is really what you are saying).