Regarding the tabs - There may have been a specific reason it was made like this that I overlooked, but I really dislike this tab system (no disrespect meant to the original designer). I also know this could be an impactful workflow change, and some people might not welcome any changes.
It isn't really scaleable when more layouts and sheets are added. I know you can close them and find them again in the project bar, but it is clunky. The frustration is further compounded when opening multiple projects - there is no real way to tell which "Layout 1" belongs to which project, and they can get mixed up. Furthermore, closing the tabs for a certain project doesn't actually close that project, and then you have to find it in the project bar, which has the additional challenge of identifying the correct one in the event that they are all named "New Project" with "Layout 1".
I always made an effort to open separate projects in separate windows in C2, and was hoping this could be default behavior. I suppose in C3 each project would be its own browser tab instead. Alternatively, maybe separate projects could have their own tabs in the C3 interface rather than each layout and event sheet.
My proposal for solving the clutter would be to have dropdown list boxes for layouts and events instead. An example from a CAD software here:
As each layout is by default tied to an event sheet, when a layout/sheet is selected in their respective list, the other box could change to the relevant layout or sheet as well. This would hopefully also reduce confusion about which layout is tied to which sheet.
I'm going to assume this particular suggestion will be a bit contentious as it involves workflow changes and more than a little bit of work on the backend, but do hope it will be considered. Also I'm sure I missed some positive aspects from a different point of view, so maybe some other users can chime in regarding that.
EDIT - I played around with the interface a bit more and I think I understand a little better now, that event sheets and layout tabs can be docked anywhere on the interface just like toolbars (This was somewhat possible in C2 in a much more limited manner. I never realized it could be done until just now, after 5 years of use though...). I guess if that is something that people will take advantage of I can see why they are tabs. I will still say that it isn't immediately clear that this is possible - even where the toolbars are stacked and have tabs they are on the bottom, rather than the top, so I don't immediately make the connection that they are treated the same way.
I do also want to second the mention that the rounded tabs look really out of place with the rest of the overall look and design.