The railways are taking more and more domestic traffic now as journey times are speeding up
Some are, but others definitely are not....example being SW England into London. For example, Flybe from EXT into LCY often cheaper than the train and definitely quicker (depending on where you're actually going in London)
And if a route to, say, a French regional airport, becomes popular, ie profitable, then FR or EZY will jump in. They get squeezed.
True again in some cases, but plenty of routes around the UK (and some into regional France) that won't ever be RYR or EZY territory.
Business travel should be riding high at the moment, so a real concern that they can't make money even in the current environment, although I do appreciate there are many factors in play, as others have described above.