I mean the Saints drafted Means when Kubiak was already our OC so they clearly felt that he had a role in this offense. And it's not like this scheme doesn't make use of bigger, not elite speed WRs. We see that in S.F. with Deebo and Aiyuk who are 4.48 and 4.5 guys.
Kubiak is just putting his best players on the field in the attack that he wants to use each week and using them in the ways that they can be used best. That's what a good OC does. When he needs to use 3 and 4 WR sets he will (and he did use 3 WR sets plenty in week One). And there are places for bigger/slower WRs in this scheme. I just depends on what kind of WRs you have and what kind of attack you want each week. Right now Olave and Shaheed are far above the other WRs so the offense is being schemed to use their talents.