Statistics NZ data shows the sector earned an average 2 per cent return on its assets in the five years to 2013, with high fixed costs and a small and low-income customer base.
The lower revenues and earnings pose important questions about where the cash for ongoing investment will come from, the report says.
Moutter said one of the report's salutary reminders was the "bits on return to the industry", with the $5 billion earned relatively unchanged in the past decade.
"It's not a rising revenue. That's supporting an investment level of 30 per cent of revenue which is stunningly high," Moutter said. "At some point, we need to [see] a stronger revenue performance to validate it, otherwise the inevitable will happen and the level of investment will shrink."
The Ministry for Business, Innovation and Employment is reviewing the legislation governing the sector, which looks set to align regulated prices for fibre and copper-based services, using a similar framework to the electricity sector.