If those shelf brackets are fixed in place and screwed in with two screws above each other that’s probably enough diagonal bracing for lightweight use, considering it’ll normally be screwed into a wall too. The fact that theres no horizontal bracing at floor level might be a bigger issue — those feet will be easily bent/broken
I seriously hate it when I accidentally build a shelf but I guess it’s just one of those things that happens to everyone at some point.
Bonus
This one significantly lacks shear strength.
If those shelf brackets are fixed in place and screwed in with two screws above each other that’s probably enough diagonal bracing for lightweight use, considering it’ll normally be screwed into a wall too. The fact that theres no horizontal bracing at floor level might be a bigger issue — those feet will be easily bent/broken
Not every illustrator is a structural engineer ;)
As long as it ends up bolted to the wall, it’ll be fine.