@GodlyVlad I don't mind that his Q can interrupt heals and actions. That's a good thing. It's cool. I don't mind the flash either. That's cool too.
What I mind is that he can do it all through walls. That's not cool. Perhaps a compromise is to make it so he can see enemies through walls using the Q, but not damage, blind or interrupt them unless they're in the open. That even fits his character of "don't look into his eyes" better.
The passive I also don't have a problem with because it's only general directional arrows on your scope. It's too powerful, but not a total problem. Perhaps it would be better if the passive had to charge up for a few seconds to work. For example, you would have to stay in ADS for 5 seconds before it would show you. And the clues could be more vague, only showing you the approximate position of an enemy, and only at close range, not far away. That would introduce vulnerability.
The other idea I had to introduce vulnerability (if the passive is left as is) would be to make it so seer is unable to detect the source of footsteps. All enemies would be silent for him, or sounds would be jumbled and confusing. That way, he could keep the passive, but it (and the ultimate) would be the only way to detect the presence of enemies.
Finally, the ultimate, I agree with you. Pulsing would make it less powerful since enemies could create traps with careful movements, such as by zigging and stopping.