I don't know if it's just me, but if Tahm teleport in, you have a good amount of time to react and move out of the way. With Rek'Sai, it seems to be much shorter. If Tahm want to use his ult to flank me, I can see him coming a mile away and easily avoid him. And since Tahm have no gap closer like Rek'Sai, there's nothing he could do. Not to mention he nede to get 3 autos off to cc someone, unlike Rek'Sai who just need to get close to knock up.