> ddos the lightning network so it won't record their HTLC when it expires
this is not even a thing. lightning network is collection of independent nodes, there is no registry of payments and channels, every node keeps their own record.
> And so while the other party will eventually see the secret on the block chain, they can't get their HTLC unlocked on the network before it expires.
why? if a party is stuck in a payment and especially if they notice they are getting attacked - they will take steps to mitigate. the moment commitment with secret is broadcast and in the worst case - the moment it gets confirmed on chain the other party will know the secret and can unlock their htlc. the risk is essentially the same as with deep reorgs - very low because those are very rare events. and the hassle is most definitely not worth the value of a stolen micropayment, which is the primary purpose of LN.