Absolutely, I'm not arguing that normal inking is faster than sdash, I'm just saying maybe getting there as fast as possible isn't always going to make up for the possible downsides. For possible example, it doesn't give you a safe escape route because even if you can escape quickly using sdash, not only is it slower than having a prepared trail behind you already, but you will also be a lot easier to spot and they will see where you escaped to. Another example is like I said above, maybe you are the only one who went down a certain trail and your teammates went down different ones so they couldn't cover it up. If you end up going down that trail a second time, it's going to be faster if you have already layed down an ink trail the first time passing it. Another example is map awareness, normal effective inking should have you looking down the horizon line most of the time, so you can generally see everything going on around you. Sdash on the other hand, forces you to be constantly looking at the ground, meaning for example an enemy could have went in a certain direction to go ambush your allies, ambush you from behind or maybe sneak into your base and gain a bunch of ink for their team with no resistance, and you wouldn't have seen it. Whereas normal inking you could have seen them, and done something about it. Lastly as far as having 2 people s-dash to mid while 2 get the area by your base, now you are getting into strategies that you would need to be in a pre-made team for, and I'm sure there will be techniques like double lines where one player inks a line while the other player swims through it, when he reaches the end he inks a line while the first player swims through both of them, and so on which might end up being faster rollouts to the middle.
All of this discussion is speculation of course, sdashing could be the go-to rollout on every map for every mode, or it could end up having too many cons and capturing middle early might not end up being as important on every map. Only time will tell once we actually get our hands on the game.