Observations

It might not look simple for a newcomer, but after learning some basic rules it becomes pretty simple. That triangle looks structurally the same in any one inertial frame of reference. If Bob turns at some point, his frame of reference is not inertial from start to finish, a turn is a change of frame of reference that changes the relative coordinates of Alice relative to Bob in both space and time, so for Bob it looks more complicated. But as long as you're looking from any frame of reference that remains inertial the whole time, it's simple.

In GR you can use not just inertial frames of reference but accelerating ones too, however spacetime in them may look warped even when it's empty and not distorted by massive bodies.

>Does "no gravitational force" model make it easier to reason about the real world problems that have gravitational force in it?

Sometimes. Not many people's "real world problems" require anything beyond Newton's mechanics. But GR provides a certain worldview, a framework with certain explanatory power.
People took atomic clocks and flew them on planes around the world in opposite directions: East and West. How to see why one clock ticked less time than the other? With a geometric approach it becomes obvious once you learn how to use it.