If you want, I can argument with a pure game-dev point of view as well if that's what you preferably want to see, won't change the outcome though. So here we go.
First of all, let's take a moment to break down the "Fighting Caustic outside of buildings" argument. Nice idea, but you seem to forget that the combat outside equalizes the chances merely. A Caustic outside has as much value as a Pathfinder, a Wraith or a Bangalore. All 3 may have more mobility and their abilities are more focused around getting out of combat and/or moving faster, in the end faster movement is hardly an advantage if you * your own aiming with that. Put 2 people with equal skill in 2 different characters, and you will rarely see someone truly dominating in an open field, reason for that being is that if you can't hit a fast character, chances are he can't hit you either. If he does, he has a higher skill value and would have killed you nonetheless. So this whole argument about "Fighting caustic outside" in the end just means "His ability doesn't really have a use there". Which I never disagreed with.
Due to Caustic being more centered around combat indoors, you will find caustics mostly there. Whenever I had a caustic in my team, nine out of ten times we sat in buildings till the ring moved, and rarely engaged in outside combat, and dominated outside combat. Which in turn has brought me among the top 5 more often than not. Take it as you want, believe it or not, in the end it's the truth and my own personal experience with him.
I already noted the logic flaw. Sure, I can take away the logic aspect and say again: Why does only the damage ramp up? Why do the other two aspects have to be instant? The immediate slowdown and the sudden blindness is what kills, because you are exposed to enemy fire, and thanks to your lack of both vision and movement speed, what other counter do you have? You can test it yourself, see how long you stay alive staying scoped and moving left and right, and then see how long you stay alive frantically moving around with hip fire. You will quickly find out that your scoped form will be shot down easily. It's about movement speed in Apex Legends. A stationary target is a dead target, as the saying goes.
Sure you may now go ahead and say that you can use grenades. Generally a beautiful idea, and I often carry 3 - 5 Grenades with me, usually arc stars. Except it doesn't really help if the trap is triggered already, plus buildings are usually large enough that the grenade can sit on a corner, and you can avoid it. It's not hard to avoid grenades, and thanks to them taking their sweet time to explode, your enemy has nice preparation time to move from one corner to another. Trust me, I threw plenty of grenades into a caustic infested building. Most of them didn't hit anything. And no, this is not lack of skill, so please refrain from using that cheap argument now.
I learned to check buildings before I enter them, obviously. Yet you still often enable a trap and have to wait for ages till it goes away. and often you will find yourself getting assaulted because setting off a trap also notifies the deployer. Because yeah, why not give the tactical even more uses. Might as well reveal people permanently because the nox is now in their system. Little sarcastic joke on the side.
I fought plenty of caustics on small space before. Q is used fast, and in the most cases blocks off any exit path, meaning you have to stick in the fight. Knowing from several past experiences in the game, charging an enemy who is aware of your presence and has their sights aimed on you is usually a terrible idea.
Again, idea here is:
- Slowdown, vision fade and Damage over time should all 3 increase in severity over time. At the beginning, 10% slowdown, light vision blur and 5 damage. After 5 seconds, a 75% slowdown, strong blur and 10 damage per second should be applied.
It's that simple.