Keep in mind that it's a Seraphon ability. The "Slann" part is for fluff, but you can teleport a single unit each turn even without a Slann. The Slann can help because you can pick Great Rememberer as General trait, thus obtaining double teleport.
Objectives help the game a lot. Without objectives it quickly devolves into basicly rock-paper-scissors as you and your opponent just keep on fielding counters. Objectives make the value of hard counters that decimate opposing units far less valuable. It's great you can destroy his horde unit, or assasinate his general instantly, but if you can't grab the objective it doesn't serve any purpose. It's especially valuable if both players have smaller armies as in a straight up fight it's usually fairly easy to see who will win depending on who counters who.
Personally, I would like 2 different kind of missions. A certain number (let's say 2/3) of matched play scenarios could work just with objectives. No matter if you wipe me, with more obj points i win. But a smaller number could have also the secondary rule that a wipe out counts as victory, no matter the obj points. After all, it shouldn't be always a smart solution to suicide your troops because "who cares".
That is indeed the only major flaw in the way objectives work.. playing completly suicidally can somehow still get you the win. Though I think house-rulling it that needing to survive is part of the objective works well enough with most of em.
I would like AoS to add in some additional objectives that are universal. Similar to how 40K has Slay the Warlord, First blood, ect. They would probably have to be worth only 1 VP each. And it might require that a lot of rebalancing take place.
I think a lot of tournaments are starting to use the secondaries in the GH book for this exact reason.
Also, objectives give value to a lot of otherwise utterly terrible troops. Skinks being a prime example. Skinks won't achieve anything except standing in the way unless you have a truckload of em. Objectives give them something valueable to stand on. Which is again doubly noticeable in small games. Skinks in a shadowstrike host in a small death match game are borderline useless, but with an objective their ability to stand in the way actually adds something, even in small games where the one battalion is really all you have.