I am not sure about other PLC's but a i am using Beckhoff with TwinCat 3 and i can see active variables in ST. Same thing with with FBD. I can't see any advantages in Ladder. Of course this is just my opinion but i feel that Ladder is very unclear.
A good ladder editor will not only show the status of the online variables, but also the status of the logic result, even in the middle of a ladder rung (* not sure if Twincat does this).
That makes it very easy to follow the logic, especially when the logic changes quickly.
And, you have to admit that it is very intuitive that you can just follow the green status through an entire rung in order to immediately understand why the rung is true or not true.
edit:
The above is to argue that the online view of ladder is more immediately informative than ST or IL.
But even when viewing or editing code offline, Ladder is better than ST or IL for logic (boolean algebra).
This because Ladder is a visual language with no need to perform an interpretation in ones own mind, whereas text-based languages such as Structured Text and Instruction List require that you read, understand and interpret the logic in your mind.
It is good that ST uses immediately understandable mnemonics (IF, THEN, AND, OR etc), but Ladder is still better. ST has a tendency to become verbose for logic code.
The advantage of ST is that you can perform more complex tasks in a compact and efficient manner.
For example, to perform loops in Ladder is possible, but will take many rungs, which may be less readable and less easy to maintain than loops in ST.