Re your last point, maybe that is a reason to target Tories more? Little doubt in hindsight that another mistake of the Swinson era was to concentrate their attacks so heavily on Labour (despite which, they ultimately couldn't even win Hallam back - one of their most ridiculous failures)
The reason why they attacked Labour/Corbyn as hard as they did was because the primary type of seat they were targeting (wealthy, suburban strongly remain), the key to winning was flipping Tory Remain voters. Being perceived to be going soft on Corbyn (who was actively despised amongst this demographic) would just have ensured these people would have held their nose and voted for the Tories. In the end fear/dislike of Corbyn was too strong and enough of these people reluctantly returned to the Tories in the final weeks to stop him, which ensured narrow Lib Dem losses in the likes of Guildford and Esher.
If on the other hand they'd openly aligned themselves with Corbyn's Labour I doubt any of these seats would've been at all close and they would still have stonking Tory majorities.
Now I do agree that maybe they didn't attack the Tories enough, however the best way to attack them would be along the lines of: 'they've thrown business under the bus', 'they're no longer the party of 'sensible' economic management' etc. whilst at the same time defending their record in coalition. Taking this line however would of course be deeply uncomfortable for the left of the party.
This is why I believe their electoral prospects would be far best served by electing Ed Davey, who comes closest to this way of thinking and thus would appeal to key demographics in most of their target seats. Layla Moran on the other hand, whilst I do think she is at least a reasonably talented politician, would appeal most to inner city Guardianista-types and would repel Tory-Lib Dem swing voters in the suburbs. The effect of this would be to make the Lib Dem vote even less efficient by going backwards in the seats they're currently close in whilst making strong gains in the Islingtons of this world but falling short there too due to Labour's vote being too strong on the council estates. Wera Hobhouse would very likely be a disaster but her winning is, I would have thought, rather unlikely.