To be fair, Support Ashe is more of an Off Meta thing than anything. It wasn't something she was made for (Mainly because Support wasn't a thing back then) nor was she balanced around it. Riot & most the community sees Ashe as a Markswoman with plenty of utilities.
She can support, even today. In the world with all of these
"supports" who are just CC-ing & poking people down despite lacking any protective abilities (besides Lux), she would fit right in. But it's not really people's go to thing, even for off meta Supports or "Supports". In fact, I assume most players don't know it's a thing & would just consider the Support Ashe trolling.
Senna, on the other hand, is BUILT from the ground up as a Support Markswoman with Support being her intend & primary role. Riot even said they would balance around support 1st & foremost.
Riot made damn sure that the whole Community know that this is a Support. Players aren't gonna be like "Support Senna? Are they trolling?" If they are, then that's on those players.
Is Support Ashe really forgotten? Or is it more the case that it is a very minor thing that was never noticed by much of the community in the 1st place?
As for Senna's balance, can we wait until she is live before we say anything? Let's not rely on the "On paper" explanation or some clickbait PBE video on Youtube. Even when she is live, we won't know for sure for the 1st few weeks because people will be learn how to play as, with & against her while dealing with people banning her because they think she's OP or, Yuumi's case, thinks she's trash & will lose them the game.