This would be useful information that would either confirm or deny an assumption made by the archaeologists. If the techniques were in use, that makes the experiment more representative of the prehistoric context. If they were not, that creates uncertainty about whether sufficiently strong reed boats were in use at the time.

The archaeologists are specifically trying to establish how the stones were transported to Tiwanaka. Whether the stones were used at other sites isn't relevant, it doesn't affect the supportive value of the boat experiment either way.

The archaeologists are posing a hypothesis about the use of reed boats back when the andacite stones were first transported. Whether reed boats are in use in modern times doesn't make a difference either way, because it doesn't tell us about those prehistoric times.

Whether other stones might be larger isn't relevant to whether the andacite stones could have been transported on reed boats. Even if there were bigger stones, we still wouldn't know where those stones came from or how they were transported, if they were transported at all.

Even if reed boats aren’t durable, the prehistoric inhabitants could’ve just kept building new reed boats to transport stones. We have no reason to think those boats would have to last for several years for the archaeologists’ argument to work.