Does Construct allow for complex game making? This is somewhere along the lines a question that all ambitious people have asked about Construct in general, not just 3. As a person who developed for Unreal Engine 3 back in 2013, that question is better handle with the word "How" tacked onto the front of it. How does Construct allow for complex game making?
If you have enough logic creation experience, then Construct will be somewhat of a breeze to prototype or build literal logic with. Cleaning up your mess is easy when it's all visual.
Setting aside how complex the playable characters are in the Dreamstrata project, we can look at something a bit simpler, albeit still rich enough in detail to remark on in regards to this subject. The piranha plant that I made in the past few days has plenty of interactions that cater to stuff seen in full body games published on console/pc and whatnot, if that's even a proper measurement to go by...
The piranha plant can be stunned in two ways, killed in two ways so far, shoot fireballs, and bite you. To stun the piranha plant, you either hit him with a forest club for the cheese or smack him while he's actively trying to bite you. On his active frames before he actually bites you is where you try to land the hit. It's a risk/reward play.
All of these things are written into under 40 lines of code blocks and is pretty efficient. A lot is being done with fairly little. You can do complex things with dutiful optimization on any platform. I happen to enjoy the tactile feel of visual scripting within Construct and hopefully the exporting options are being rounded up with the same level of dedication as Construct and Dreamstrata, so that this project will be able to launch to multiple places, allowing as many players to play this as possible.