Isn't content from Mastodon federated across the instances? Meaning that LW could just open an account on any Mastodon server (not their own, to avoid to handle both at the same time in case of issues)?
Or are you saying that Mastodon is as DDoS vulnerable as Lemmy, making the server that would host the LW account a DDoS target?
Edit: you edited in the meantime, but I guess our exchange still makes sense