If you're in the position to be casting shadowblade, you're generally wasting your spell slots. There are very few builds that can take advantage of shadowblade that don't have better options. By the time it becomes a better option, you have shit like Haste you can cast. The only exception is if you're attacking in darkness, in which case its definitely a decent option. In general at second level I'd rather be concentrating on something like a web spell over shadow blade. But in some cases yeah shadow blade is a better option.

And I usually don't consider viability of builds beyond +1/+2 weapons, its entirely dependant on your campaign/DM. If you can get a decent weapon, then you're right.