You want to have a character walking on the screen

3dgs

you load a model in the editor
You create an Action in SED :
ent_Animate(my,...);
c_move(my,..);
you assign the Action to the model

Unity3d

you load a model in the editor
you create a script :
transform.Translate(...);
animation.Play("Walk",..);
you assign the script to the model

Truevision3D

The engine supplies a TVActor() class

you instance your model
TVActor myModel;

You load the model
myModel = TVActor.Load(".."):

In the game play you write
myModel.Move(...);
myModel.PlayAnimation("Walk",...);

Are exactly the same stuff for you ? I dont think so

In my opinion TrueVision only allow a true traditional OOP
Unity3d is on Component side, Components are also classes, if it is what you meant
3dgs is something in between
Actions in my opinion are components created by developer
3DGS is probably more flexibile than other engines but I find the code style quite ugly...personal taste of course