@Virtual Bob, sorry, I was on my mobile and missed the "being" making it into a progressive. Still not a terribly difficult concept, and where languages lack a progressive, then your translation job is easier. Rarely will the progressive in a future perfect progressive be so integral to meaning that you must find a way to express it. As Putin so very kindly pointed out, "in speech, nobody uses [future perfect progressive]. If you read a textbook or a novel, sure." In speech, yes, we use gerunds all the time, but I really don't think the concept is hard. On-going action. Not that hard. And when a non-native uses the present active instead of the present progressive, big deal. We know what they mean.
As for the helpers, I read Ancient Greek on a daily basis. Don't tell me Russian's tense system is easier due to verb modifications. Helping verbs are easier. Period.
I did not claim that prepositional confusion rarely obscures meaning, I claimed it rarely /changes/ meaning. For example, "I will be there on time" and "I will be there in time" is prepositional confusion, but meaning is not obscured. They carry different connotations, sure, but in a fuller context, which was intended will be clear. Another example, "I took the statue in the garden" and "I took the statue into the garden." The meanings are very different, but not so vastly that they lose meaning in the right context. I'm having real trouble thinking of an example that changes meaning even in context. I'm not sure a native speaker would misunderstand preposition confusion when in context. (Obviously, outside of context, preposition confusion is much more problematic.) As for prepositions adding complexity to language, recall that all languages have prepositions (or postpositions). Saying that English prepositions are hard is a non-statement. (I would argue postpositions are harder, probably due to my Indo-European heritage, and especially difficult in Japanese, but then I only have passing familiarity with Japanese particles.)