From what I can tell, one of the main goals of IPFS is decentralization. Anyone can be hosting the file you want and it will download from any of the peers. Does OnionShare do this?
As you mentioned, I've also found IPFS to be fragile, particularly in that it is unlikely for stuff to stay up reliably, as ironic as that is. If I'm trying to host a website with not too much traffic (nobody else replicating), I have to keep my computer online or it will become inaccessible.
There's an annoying misconception that IPFS is "free storage" - it's not. If you care about something sticking around on the network, you need to take action to ensure that happens: either as an individual pinning it to a persistent node you run, as a developer paying a distributed pinning service to host your dapp data, or as a community creating a social agreement to all peer their nodes to replicate each other's data. All these solutions are doable today, but you shouldn't expect others to host your content for free (if it isn't popular enough for other people to be proactively caching it). IPFS is the distributed network for addressing files, you have to bring, buy, or share your own storage - anything else (ex forced hosting of content you don't choose) would have problematic liabilities!
IIUC, it's onion-routing request traffic to your computer, but your computer is still acting as the sole server of the website. Turning off your machine gives incoming requests nowhere to resolve to.
> it is unlikely for stuff to stay up reliably, as ironic as that is
Well, it's kinda inevitable with these systems, since there's limited available space. Freenet lets you "insert" data into the network (copy to other nodes) and disconnect your computer, but if nobody requests that data, it'll also eventually disappear from every node.
As you mentioned, I've also found IPFS to be fragile, particularly in that it is unlikely for stuff to stay up reliably, as ironic as that is. If I'm trying to host a website with not too much traffic (nobody else replicating), I have to keep my computer online or it will become inaccessible.