Yes there are alternatives but not tested yet on mainnet

Depends on the kind of relays users prefer to use for a round.

Example: If users prefer to use paid relays in a round then cost is decided by nostr relay

Also encrypted channels right now are not implemented, which it would help in reducing DoS vectors

Interesting that you consider "no fidelity bonds" to be a feature. Those were added to joinmarket to improve sybil resistance. Does joinstr have an alternative method to reduce the risk/increase the cost of a sybil attack?