I think most player are so used to getting elder in normal mode, so people don't see dragon soul in same light.
Afaik in lolpc, dragon soul is contested the same way as the elder in wr as of right now.
Though i still agree that timer after first dragon should be lowered to 4 to 3.5 mins. I have played 50 plus elemental and rarely got a soul, as most matches were mostly over by the time soul dragon was up.
Plus even with the soul, late game it hardly matters, as everyone is full build. So tweaking the buffs to give certain advantage should be considered again.
Got elder 2-3 times and the 20% execution is kindof too strong, maybe that's the intention to begin with.
But in very close matches, where everyone is trying hardest to pull a flip, outsmart other team. Elder just ruins the late game neck to neck rush.
Elder is designed to make sure games end. The soonest you can see it is 20+ min, and like you said it can spawn much later than that if the other team gets a dragon. So a long close game still needs to come to an end, and forcing an Elder fight should be a good way to do that.