1. Construct handles scaling just fine, just make your assets at a size that doesn't loses too much quality when scaled up or down.
2. Ads on iOS arent working at 100% right now because of the GDPR changes but I'm sure scirra is working hard to fix it.
3. When making an iOS game Construct3 can export it as a xcode project and then you open it in Xcode on your mac to produce the ipa.
4. Construct uses web technology (HTML5/javascript) wich is constantly evolving at quite a fast pace and this obviously brings some cons but pros as well.
Personally I'm excited to see what kind of performance and other improvements Constructs new runtime brings when it is ready for "live" use.
I do own a full set of GameMaker Studio 2 and Clickteam Fusion 2.5 but Construct3 is so much faster and easier (and fun) to use so the other 2 aren't even installed on my computer right now.
Don't know if this will help you make a decision, good luck any way with what evver you choose :)