Yes, it BENEFITS the buyer, because gives him/her an option to buy, not an obligation.
The "terms" that you mention in a lease contract, could be also as negative, with other type of standard leases, not necessarily with the lease-to-option program. In other words, a disadvantageous lease agreement could be wriitten, whether or not is a Lease with option to buy. So, in your example, when you put specific posible situations (but not general situations), creates a fallacy. The fallacy, that a Lease with Option to Buy is negative.
In my life, as a lender, 13 years, I have found that certainly is mostly advantageous for the buyer, if the buyer decides to use his/her option. What I have found out is, that most of the time, I'd say 90% of the time, the buyer tought that the whole 100% of the monthly payments were going to be used as the downpayment; where they were wrong. And that was entirely, because the realtors that "helped them" to write the contract, was ignorant about how did it work, from the lending side.
A market price for the lease with option to buy, is just as any other exchange market in the whole world. Because under your philosophy, there would not exist Options, Futures, Swaps, Warrants, Factoring and Forraiting (Financial Instruments that work more or less under the same underlying principles than the Lease with Option to Buy).
The price for the monthly lease, is dictated by the market. Most people pay a plus-value when they have subjective reasons (such as fashion, location, need, etc) to agree on determined contract. A good and experienced realtor, should explain, and help to understand the key aspects of the a Lease with Option to Buy agreement; if it is disadvantageous would be because of the guidance from the real estate agent.
I am currently helping to finance, a friend of mine, that entered in a Lease Agreement with Option to Buy, 2 years ago. The seller is an absentee owner, and when the expectations that the Real Estate Market were going to keep stagnant, for the next 10 years (from 2007), I believe it was thought that the set price was sufficient enough. But now, that prices have been gaining some apreciation, or there is scarcity of supply (properties), by the time she closes, she will have an apparent equity of at least 55K. Does this serve to sustain that this type of agreements are definitely advantageous? No. Depends of the professional advise obtained.
Usually the Lease with Option to Buy, is more effective when there is a real motivation from the seller, to minimize the "Wear & Tear" of the property, and decides to transfer the use (not ownership) of the property to someone with "Homeownership" mentality, and that if after certain time the tenant should decide to purchase the property. This contracts are more common in downturn markets. Not too common in upturn markets.
Last but not least, "BUYERS BEWARE" when choosing a REAL ESTATE AGENT. Mrs. Debra Rose seems to be very professioanl.