NIP-44 is just the encryption. The DM protocol is NIP-17 with NIP-59 and NIP-44. No one uses NIP-44 by itself for messages.

1. NIP-44 has padding for fixed message sizes. 2. NIP-17 DMs is giftwrapped by ephemeral keys in public, so repudiation/deniability is provided as well. Gift wraps can even use random alias keys as receivers. 
3. The connection graph is not visible unless the NIP requires it to. 
4. Break-in protections exist on the wrap. Breaking individual messages does not reveal the main nsec of the Nostr user. The only way the break-in can work is if the attacker gets the long term key or seed, which is also a problem for other E2E apps.