First of all, you can prove any single file with succinct merkle proof that is the whole point of merkle trees as opposed to stream hashing all files.
Second you can still OTS merkle roots.
I just want you to stop and start thinking for a minute if there is a single person on earth cares about accurate timestamping of shit posts other than you as a protocol designer.
I am not telling you you shouldn't use OTS, it is not adding much cost, but I am definitely saying no body gives a fuck.
