If you go to CEDR BA won't have the chance to raise multiple rounds of arguments - you'll claim, they'll issue a defence (or settle), and you'll have the opportunity to respond to their defence.

In this case I'd be arguing in the first instance that the mysterious resourcing issues at LHR are not exceptional given that it is BA's home base and that they should be prepared for those. In addition the BOS night curfew is blatantly not exceptional since it is a routine nightly policy at BOS, not an unexpected one-off. As you suggest, it is worth flagging that as BA are fully aware of the BOS night curfew, it is their responsibility where necessary to prioritise a BOS departure to ensure that the curfew isn't an issue. And as others have mentioned, it is worth noting other flights from the UK that reached BOS that night, presuming that they did.

I would then note that even if BA's explanation for exceptional circumstances was accepted, there was nothing stopping them operating a delayed flight the following morning - hence, in circumstances where a delay was unavoidable, a cancellation certainly wasn't, especially at their main global base where they could reasonably be expected to be able to provide an alternative plane or crew if necessary.

If BA choose to defend rather than settle you'll then have the chance to review their arguments and think about how you might want to respond to them.