I've got 2 arguments to left it as is:
1. If there's no template for the block it's better to remove it. So when compilation fails it's like a kind of linting saying "there's something wrong with your code, go and fix".
2. there are a lot of templates with just one custom mode and it's convenient to write them in "dot-notation": `block('bla').js()(true);` or `block('bla').content()(/* ... */);` so having parenthesis will disturb.