Reusability is certainly an integral part of the long term goals of Starship. In fact it is enough of a priority that tests related to landing have been included in each Starship test flight. However the idea that the test program is driven by the need to prove landing capability does not match what appears to be the strategy of the Starship test program. And in fact it was not the strategy for the early Falcon 9 program, which had the successful and safe launching of payloads to orbit as the top priority, with development of booster recovery capability as a secondary priority. Even though from the beginning booster recovery was an important long term requirement of Falcon 9, as it is with Starship.
Like Falcon 9, Starship can conduct successful missions without recovering the Starship, or the booster, or even neither. You are correct though that for long term cost benefit, and I would add schedule benefit, successfully landing and recovering a high percentage of boosters and Starships is a requirement for maximum program success. Crewed launching and landing is a separate topic, and in my opinion is not a given in the Starship program, which I suspect can be an economically successful program even without launching crew.
Looking at the Falcon 9 test program, there were the Grasshopper and FR9 Dev1 single stage launch and landing test flights which in some ways can be compared to the Starship high altitude tests. Although the Starship tests were much more ambitious, each of them reaching at least 10 kilometers, compared to the highest known FR9 Dev1 test flight of 1 kilometer.
I realize that you do not consider the SN15 flight as having successfully landed, but in fact it did successfully demonstrate landing capability. A small fire occurred after landing, and due to the lack of fire suppression capability at the landing site the fire burned itself out after about 20 minutes. Presumably SpaceX determined the cause of the fire and has made the needed corrections, and apparently felt that the landing was successful since they decided that there was no need to perform another landing test.
I think it’s worth quickly going through the Falcon 9 landing attempts leading up to the first successful landing on the 20th Falcon 9 flight. First as a reminder of the early struggles that have in some ways been forgotten. But also to highlight that as a launch vehicle Falcon 9 had tremendous success in spite of repeated failures attempting to recover the booster. The pattern that we see with Falcon 9 may possibly portend how the Starship landing tests will go. Although with their prior experience SpaceX may possibly have success landing the booster and recovering Starship from orbit much sooner than the 20 flights that it took Falcon 9 before its first successful landing. It should also be noted the number of Falcon 9 flights that did not attempt to recover the booster. As SpaceX made ongoing modifications to the boosters to enable successful recovery, they did not allow it to hold up the pace of satellite and Dragon capsule launches.
The first two Falcon 9 test flights in 2010 were considered a success, the first flight put a test payload into the target orbit, and the second flight successfully launched the Cargo Dragon COTS Demo 1 flight. Even though in both test flights the attempted booster recovery by parachute failed when the boosters burned up during reentry.
The next three Falcon 9 flights successfully delivered their payloads to orbit, however no attempt to recover the booster was made on these flights.
On the sixth Falcon 9 flight, after successfully launching a satellite, the booster attempted a water landing, identical to what the first Starship test flights are doing. The booster lost control shortly before reaching the water.
The next two Falcon 9 flights successfully delivered their payloads to orbit, however no attempt to recover the booster was made on these flights.
The next two Falcon 9 flights successfully delivered their payloads to orbit, and both boosters made successful water landings.
The next two Falcon 9 flights successfully delivered their payloads to orbit, however no attempt to recover the booster was made on these flights.
The next Falcon 9 flight successfully delivered it’s payload to orbit, however the booster failed an attempt at a water landing.
The next Falcon 9 flight successfully delivered it’s payload to orbit, however the booster failed an attempt to land on a drone ship.
The next Falcon 9 flight successfully delivered its payload to orbit, and the booster made a successful water landing.
The next Falcon 9 flight successfully delivered its payload to orbit, however no attempt to recover the booster was made on this flight.
The next Falcon 9 flight successfully delivered it’s payload to orbit, however the booster failed an attempt to land on a drone ship.
The next Falcon 9 flight successfully delivered its payload to orbit, however no attempt to recover the booster was made on this flight.
The next Falcon 9 flight was not successful due to vehicle breakup and loss of a Dragon cargo capsule.
The 20th Falcon 9 flight successfully delivered its payload to orbit, and the booster successfully landed at the LZ-1 landing facility in Cape Canaveral.
The first landing success was in December 2015, more than five years after the first recovery attempt. And yet the Falcon 9 program was already very successful by then. After the first landing success there have been six more failed landings, and 204 more successful landings. The last landing failure was in February 2021, as of July 7th there have been 131 successful booster landings in a row.
The Starship test program seems to be starting out with a similar strategy of concentrating on flight operations first, with landing tests a secondary priority.