With operating losses of US$2 billion (NZ$2.82b) a year - more than any other start-up in history - Mr Horan argues there is "no evidence that Uber's rapid growth is driving the rapid margin improvements achieved by other prominent tech start-ups as they 'grew into profitability'."
In fact, the "absolute magnitude of losses has been increasing", he writes.
According to limited financial information provided to investors, for the year ending September 2015, Uber posted losses of US$2b ($2.82b) on revenue of US$1.4b ($1.97b), a negative 143 per cent profit margin.
"Thus Uber's current operations depend on $US2 billion in subsidies, funded out of the US$13b ($18.31b) in cash its investors have provided," he writes.
"Uber passengers were paying only 41 per cent of the actual cost of their trips; Uber was using these massive subsidies to undercut the fares and provide more capacity than the competitors who had to cover 100 per cent of their costs out of passenger fares."
The Financial Times argues Uber's "entire business model [is] questionable".
"This is critical because it suggests we're dealing with a charity case in disguise," the paper notes.
"Silicon Valley elites justify the subsidies in the name of monopolistic growth expectations and the building of 'eco-systems'. They believe if monopoly status is achieved, profitability will follow naturally from that point.
"[But] there is no reason to assume Uber's obliteration of local competition across the planet will create a sustainable business in the long term.
"Costs are costs, even if you're a monopoly. As long as people have cheaper alternatives (public transport, legs), they will defect if the break-even price is higher than their inconvenience tolerance threshold."
Mr Horan said claims in recent media articles that markets in developed countries were expected to generate "billions of dollars in profit" in coming years would require fares to quadruple.
"[The] US$4b ($5.63b) profit improvement needed to convert today's $US2b losses into a US$2b profit would require some combination of the most staggering efficiency gains in the history of private enterprise ... and humungous fare increases (fares would need to have quadrupled to have produced a $US2b profit in 2015)."
The Financial Times points out that "with the economics of the core business model looking that bad, small surprise Uber is currently preoccupied with pivoting its way to viability", with initiatives such as carpooling, "optimised pick-up points", and the "equally questionable" UberEats.
"[Customers'] preferences are ... subtly massaged and managed with discount incentives and other behaviour moderating mechanisms (like crappy app navigation which makes it impossible to opt out of a pooled journey)," the paper writes.
Mr Horan argues that Uber's refusal to consider an IPO "may best be explained by the recognition that publishing detailed, audited financial data confirming these massive losses and the complete lack of progress towards profitability could undermine public confidence about its inevitable march to industry dominance".
However, Bloomberg reporter Eric Newcomer, the original source of some of the financial information cited in the report, said the analysis was "flawed". Newcomer said Mr Horan was mistaken in claiming the losses from Uber's China venture were not included in the financial figures.
"Uber's first-half of 2016 losses included China," he tweeted. "Uber owned 87.5 [per cent] of Uber China. Losses WERE consolidated. Support Uber scrutiny. Agree Uber is so big it should share its numbers. But this analysis seems flawed."
Uber declined to comment.
