First, I've got proof no. 3. I can offer a nice 4 argument proof, but you wouldn't let me provide it. Second, I tried proof no. 2, where I'm offered words like given and algebra I have no use for.
To make a system like this right it needs to be deductive and have a large library of concepts. Getting this right is complex enough to be a PhD project. Properly scoped could be done for MSc.
If you treat it as a kind of puzzle where you have to arrange the given blocks to form a valid proof, it's not so bad. However, you should at least be able to reorder independent statements, and reasons should include references to the previous statements they depend on, e.g. in proof 4, "<A = <D" follows by "Substitution" only because the previous statement is "<EBC = <A and <ECB = <D". In longer proofs you may have to refer to something proved further up, and requiring the student to give the reference would be a further check of their understanding.
Similarly algebra = "solve for algebraically"