[2022] Why does scarab catching feel so ... broken?

Heya, I can answer these

1. Yeah, success chance (something between 98-99% at level 99) - additionally, your success chance decreases a bit with each scarab you stack
2. I would have said this is intentional, but as you've said other boosts/bonuses work with it this sounds like an oversight - I'll look into this :)
3. TL:DR; Engine limits. I believe there's a cap of clicking 7~ tiles away from your character before you move. Unfortunately this is something that could have been planned better - it's not a problem I gave any thought to, as during dev I was working on scarabs on a test mapsquare, with a smaller pool (and thus was not running around the entire pool). By the time the scarabs were moved into the actual environment it was more or less finished, and I hadn't anticipated it to be as large a problem as it is. Learnings for next time!
4. Originally you could - this was changed due to a nasty exploit (that couldn't otherwise be fixed without a system rewrite)

That's a reaaalllly good question that I'll have to look into (same for controlling nodon cannons I believe?) 👀 Iirc the exploit used both adding and removing unfortunately

Not yet, but I haven't forgotten! I'll be looking into it during game jam at the start of next month