I think something is more complex the more rules it has. For example, if every instance of "is", "am", "are" is turned into "be", English would be less complex because there would be less rules. e.g. "I be happy. You be sad. He be bored". I believe this is how mandarin does it.

Each of those conjugations has a different subject. By standardising them all into the same word, it's possible that you make it more efficient for the producer (speaker or writer), but the receiver (listener or reader) has to put more effort into understanding.

This is why languages evolve. If something is pointless, it tends to disappear from the language over time. And it's why artificially produced languages just don't seem to work - they are perhaps more efficient at communicating across boundaries, but less efficient in the primary use case of communicating within a boundary.