It's not weird that mages end up with LB. They wear lighter armour, so they have higher EV, so riposte is supposed to trigger more often, even when they are actually casting spells. Conceptually, riposte was a way to encourage using LB with lightly armoured characters. So that's what was meant to be.
I think that long blades could have both SH and riposte. Make it the default weapon you want for
passives that help you while you are doing something else, like casting spells. The choice then is between LBs, stat enhancing unrand weapons, and enhancer staves. They also should be helpful for draconians.
The distinction from protection would be that protection isn't a passive any more.
The one thing I dislike about riposte is that it seems to generate special cases. So it apparently doesn't chop hydra heads off, which I only noticed today by looking through the website (
https://github.com/crawl/crawl/commit/4d40d61ba56a ). It also triggers constriction, and I think Duvessa once said that it changes the target you are constricting if you are a Naga. The other thing is just how hard it is to understand how much damage it makes, and how much influence it has, and how it compares to e.g. m&f or a lajatang. If there were numbers instead of !!! to tell the damage, it would be much easier, especially because of the influence of different brands on riposte damage.