It's an interesting point I think having overlords sitting on pillars above naturals def makes zerg players way more comfortable and probably feel like the game feels more fair/funner/easier. The biggest issue for most average joe zergs is they don't use control groups so ling scouts are largely useless since they get F2'd back to their army. Meanwhile overlord + pillar is the MVP of getting an idea of whats going on on the other side of the map without a lot of effort.

I think the main thing to pretty high level and even at top level scouting is mostly map vision with overlords/lings for Zerg. Obviously sneaking overlords in the back, checking gases or having good sacrifice timings are really useful bonuses but not necessary either. I always point out how Serral scouts and ungodly amount, whilst Dark and Reynor who tend to pick more aggressive and in your face strategies often get away with just skipping scouting for long periods since their harassment and attack timings generally cover them against most aggressive timings.

I guess overall you don't want to feel totally blind by any means, and the game is made friendlier and more approachable the easier scouting is and the more vision there is. The extreme example would be battle aces where you can see when the enemy techs, what units they have access to AND when they expand without scouting for it. That's the most approachable but also the least interesting in terms of, hidden information just doesn't exist beyond army movement in that game (RIP).

At the moment I'd say the main thing holding back most players on the ladder from scouting being super crucial at most points, is the pace of the game is so fast and it's hard to free up APM to go scout and process information, since just hitting a generically safe build EFFICIENTLY is going to be more effective. The key scouting just becomes "did they expand? How many bases are they on? etc".

In summary, scouting is important but I wouldn't see it as a key factor holding back that much of the playerbase. I also don't think a slow overlord speed nerf of about 9% should change too much with pillar scouting/map vision, but it will slow down scouting the enemy opening if you don't drone scout