Thank you!
Yeah visual clarity is something I'm working on, by reworking the UI and making the background darker notably. I'll also introduce the mechanics over time in the actual game which should make things less confusing.
As for the swapping issue, it really depends. I would argue that selecting more than 2 pieces at once makes it easier to both clear more blocks at once and line up over 3 pieces. Lining up 4 and more pieces gives you energy, which allows you to use relics if you have any equipped. Once again this is something I need to explain more clearly. That being said it could be interesting to look into some incentive to clear multiple chains at once... I'll keep it in mind!
And finally about the discarding mechanic, to get items to appear in the overworld, I can't really think of a better way to do it... I recommend using the middle mouse button for quick discard over the drag & drop, but if you were already doing that I'm not too sure what to do to improve it. If you have any suggestion, I'll gladly take it ^^