Toddler, what exactly would you like to do in constructor and update functions?
It is true that in every OOP language you have a very useful constructor (and desctructor) function which is triggered when instance is being created, but in C2 you also have "Sprite -> On create" which is exactly the same.
I don't know what do you mean by "update" function, because there is no such thing in programming like a predefined "update" function. So I believe you need some custom actions here. This also can be easily done with Construct 2 functions. You can build your own function with parameters and set return value. You can also call it "update" . It is also worth to mention that you can call them with callbacks as well.
Regarding entities. You can set instance variables for your object, and their values might differ in each instance of your object so it is exactly like Class/Object in OOP.