Sorry for such a late response. My computer faced multiple problems throughout the weekend resulting in me not even able to connect to the internet. If you see this, it means it is resolved.
Interpretation
Keep in mind, the 3PO line does not refer to the C line of Cybot, and the R2 line does not refer to the entire R-series including R1 through R9. Also, we are comparing the average R2 droid with the average 3PO droid as phrased in the title. R2-D2 and C-3PO are two war heroes that simply exceed the expectation of the work done by the average droid of either type, therefore they are outliers and are not specifically being discussed here unless to showcase mechanisms and possible functions that are documented with the most clarity in films.
Arg1: The 3PO line had LESS substitutes
The 3PO line, produced by Cybot, began its production in the old republic era, at 112BBY. Its production didn't end until the New Republic era, AFTER EP6, being replaced by an enhanced C-series. Therefore, in this span over 100 years, effectively all work that is exclusive to the 3PO line are fulfilled by the 3PO line.
The 3PO-series protocol units were considered the most advanced Human-cyborg relations droids in the market for over a hundred years.[
1]
In other words, the 3PO series effectively monopolized(or at least holds a large share in an oligopoly) in the communications industry for more than a century. It is almost NOT competing with droids Cybot itself produced that is a different line, except for maybe the TC-line, which doesn't really have anything crucially "better" than the 3PO line and is overall not as popular.
This is different for the R2 line, which had numerous replacements before the end of Endor. Namely, the R3, R4 and R5 units. Each of these three does something better than R2, rendering not only R2 good at many things but not the best at everything, but the R-series essentially competing with itself, possibly more than the 3PO competes with the TC of Cybot. Of course, this does no dent to the profits of IA who produced the R-series, however, this would render:
- R2 less desirable in conditions with antigravity, such as in many advanced spaceships, than R4 units.[2]
- R4-units are employed before 22BBY and has been already used by the Jedi Temple, as shown in Ep2, Obi-Wan and his starfighter. R2-units has probably already lost its monopoly on astromechanical functions.
- R3 more desirable in conditions where large memory storage is needed than R2[2]
- Among less wealthy customers, R5-units are more desirable as they are cheaper.[2]
- We can get a live example of this: Uncle Owen at the start of Ep4 initially chose the R5 unit and C-3PO to work at his moisture farm. Until the R5 unit broke down to help a brother out(R2-D2), Uncle Owen would have not even wanted the R2-unit.
- In the same example, C-3PO was seen speaking about his ability to understand and speak Bocce(a language on Tatooine, despite that he never intended to land on Tatooine in the first place if not for evading Darth Vader's inspections) as well as being able to operate binary load lifters, something that is expected for a skilled human to do. Essentially, C-3PO doubles as a big-brained human.
Arg2: Communications vs Astromechanics
In Ep4, Obi-Wan has commented on the nature of R2-units: They are dime a dozen. This line was written before the prequels were fleshed out, so this line can be implied to refer to the condition on Tatooine. The problem of this is:
- Most people on Tatooine have no need to fly to other planets, at least not with an aircraft that requires R2-units.
In what aircrafts can an R2-unit be inserted into? You guessed it, personal starcrafts such as X-wings, which definitely are in the posessions of armed groups(such as the Empire and the Rebel Alliance). Not even the fastest YT-1300 freighter in the galaxy(owned by Han Solo) requires an R2-unit to fly. Therefore, the R2-unit is dead to Tatooine: Well not exactly, they are basically mechanics, normal mechanics fixing normal stuff. The average R2 unit is definitely not used to the full potential.
Even on Tatooine, a remote desert planet with maybe 2 or 3 heroes, R2-droids are commonly seen. Such can be assumed to be the state for many other remote planets as well. A large demand of R-series droids(which mind you, the R2-droids only take up a portion, the rest is filled by such as R3, R4 and R5) possibly comes from the numerous "poor planets", so does possibly 3PO droids.
However, since 3PO droids can translate between millions of languages, given the amount of different species and cultures existent in the galaxy, They are indeed useful. 3PO droids are also capable of operating machinery such as Moisture Vaporators, effectively reducing R2's exclusivity to even less, as 3PO units are indeed capable of operating many machines that humans can operate.
In the end, the 3PO droid exclusively fulfills all translation and communication works(while R2 speaks in a tongue that in itself is hard to understand initially) compared to R2, while R2 exclusively only fills a small amount of mechanical works which are just utilizing the toolkit it came from(and they might as well be substituted for a 3PO droid with tools, as 3PO droids can operate even starships as seen in episodes 3 and 5)
Conclusions
- The R series competes with itself more than the 3PO series competes with other Cybot lines.
- The R2 is the least exclusive droid out of the R2 through R5 lines. Therefore, it is effectively reduced to being a normal space mechanic for any entity that can afford R3, R4 or R5.
- The 3PO has no such weaknesses for decades and are considered to be the most exclusive and the most able droid of the field.
- A large portion of the R-series' market does not effectively use its full potential, rendering it just a moving tool kit for people that has no demand of moving outside the home planet.
- 3PO droids can operate starships, operate moisture vaporators, and can use tools. This leaves a very small set of things, for the average droid, that the R2 can do while the 3PO cannot.
- 3PO droids can translate between millions of languages, which is almost always useful.
Sources
Unfortunately, the computer issue means that pages like Wookieepedia cannot correctly open, therefore the citations here is suboptimal.
- Star Wars Episodes 2, 3, 4, 5
dang... This might put RM into the no. 2 spot.
Believe me when I say that I can barely open Wookiepedia pages with the internet I have.
Don't ask, if you think it is irrelevant, disprove it. This argument was typed late at night after 3 hours worth of attempts for fixing my own computer.
How is your first contention even relevant to the debate? LOL