I personally think most ults in the game are 20 seconds too long. You shouldn't be able to kill someone and have your ult be up before the lane gives them a chance to fight.
Think about it: X champ ults you. You two fight for maybe 15 seconds. You die. You spend 23 seconds dead at level 6. 38 seconds have passed since the ult was used and you just respawned.
Summoner's Rift is measured to be 19,000 units from Nexus to Nexus. Using trigonometry, we can calculate the distance from Nexus to corner to be about 13,000 units. At 350 movespeed, that takes 37 seconds. If you're mid, only a 27 second walk.
So just fighting, dying, respawning, and walking back to lane has consumed 75 seconds. Most of these champions have 90-110 second ulimates at rank 1. This means even with no CDR you literally get one minion wave after arriving to lane before you get ulted again. If the person has CDR runes and rushed a 10% CDR item, they could easily have the ultimate up as you arrive in lane.
Yasuo has an 80 second cooldown on his ultimate at rank 1. You can basically guarentee that it's up as you arrive to lane if he killed you.