I'd run Survival primarily because, given enough time, the game finally scaled to where you were at and then beyond. 50+ minutes on high level infested missions is just wall to wall assholes to kill and its glorious, especially for me. Then you go up another level threshold and suddenly the damage is very very real and you gotta play a lot tighter. Up another level threshold and you're in one shot territory.
Yet even that was underpinned by 40 minutes of trivial boredom. And I ran so much Apollodorus to grind out XP that I started getting sick even at the thought of doing survival.
But I don't think I agree about being rewarded better resulting in less obsession with speed running. People speed run because they enjoy the rush and the game is built for it. I think optimizing the grind is an important but maybe secondary part of it. So giving out chunkier rewards would just result in people getting more rewarded for the same behavior. To me it's just a function of the game handling and the optimal enemy bullet sponginess vs. their numbers to produce the right conditions for gotta go fast. When a blurt from your best gun can kill 1, 5, even 10 guys at a time and that's what the game builds itself around, that's what the meta becomes, is running around doing that as fast as possible. And when you know most of those enemies aren't going to pile up at your back and threaten you, or will spawn endlessly no matter how many you kill, there's not much motivation to spend more time with them than you need to unless the mission mandates it. I'm not a speed runner in games by nature, it's just not my style. Yet even I gotta go fast in WF, because it just feels right and because most of the time there's little point to doing otherwise.
That said I remember back when my friends and I were scrubs around Update 10 maybe? and doing high level voids we weren't ready for, we'd all be hunkered down in cover together trying to snap off shots and not get our faces taken off. Powers, energy? Useless at that level of difficulty. And it was actually a little fun. I think if a) levels were smaller b) the average enemy was way tougher and c) there were fewer of them you might get slower pacing out of the game. But WF is pretty much known at this point for its fuck off yuge tilesets and dozens and dozens of enemies spawning at a time or being lined up for you to knock over. To really change that to produce slower pacing feels pretty impossible at this point.