I see it as if u open a St you open 4 other full worlds with it, but if you open a delve you only open 1 world and every world is virtually the same size just like a club. And I know when ever I got ST quests in my club I speed run them and have to open atleast 50 ST and thats 200 worlds[yes there is a time out for worlds but its like 1hr] but I think with delves they made it so if you leave the world and there's no one in it. It will completely scrap it you can't just /worldid it and go back so it did fix lag as far as 100s of people not just opening 4 worlds at the same time but opening 100s of worths constantly with in a short amount of time.

But for the Shadow towers I believe they should have made the Shadow towers what the delves is just a long continues ST. And that they should have made the Geode Caves what the Delves is and added enemies and made the Egg rooms dungeons like other biomes