It is likely your 'every tick' events have little or no performance impact. If nothing at all on screen changes (as you say is the case when you disable the events), Construct 2 does not actually redraw the screen. Most games spend 80-90% of their time rendering, so if you measure the framerate when nothing is moving (and therefore the screen is not drawing), the result is meaningless. It will basically be doing nothing at all apart from updating the FPS counter. I assume you are enabling an event which causes a per-tick change in the display, which causes rendering every tick, which then results in a real framerate. This may make it look like a single event is having a huge performance impact, but it is very unlikely this is the case. In general you shouldn't worry about event performance anyway.
Note that moving offscreen objects, or moving an object then putting it back in the same tick, still results in a redraw. Construct 2 doesn't try very hard to detect is nothing has visually changed, because doing so accurately is extremely difficult and most games redraw every tick anyway.
For the record, C2 does not use a multithreaded engine right now.