To answer your question. Yes, and no. You can put in a new rag joint which is the weak link, however over time it will wear out to where you would be replacing it again, also it does flex which is why even in its newest state its not as positive and without slop as a universal joint is. Additionally on 4x4 trucks with larger and wider than stock tires the universal joints tend to help with a more positive feel driving over a flexing rag joint. The frame flex you are getting is not a whole lot.
You also have to remember that large volume production vehicles are designed and built by committee. What is meant by that statement is simply this, the bean counters look at things like cost for every little item that makes up a vehicle. Example can the engineers design something that would be adequate using 3 bolts instead of 4 to attach it, saving the additional 1 bolt x how ever many vehicles etc.
Thats just one example, but they do it with everything. If i was a betting man I'd probably say that replacement lower rag joint part number probably has a passenger car and light truck vehicle range of at minimum 40 years. Why? Because it worked good enough for stock stuff, and the tooling money was already spent to punch out this part. Also the design is good enough to get the vehicle out of its warranty period without problems. Vehicles are designed with planned obsolescence in mind. Average life span is supposed to be 10-15 years.
Now getting back to the u joint issue. The rag joint does work pretty well for its initial designed job, my buddys 55 chevy had one, my 60 elcamino had one, my brothers 87 monte SS had one. It was there for one reason only, it was a "cheap" solution to a problem. Think like a bean counter again. A pair of universal joints is more expensive than a rag joint. Both get the job done. How many thousands of these trucks was GM pumping out of 3 different factories at this time? Between Chevy and GMC i venture a bet it was at minimum 350,000 trucks a year. When i special ordered my 1994 new i waited 22 weeks just to have a vin number assigned to it. And another 6 weeks for the dealer to receive it in.
Lets use that 350,000 vehicles as our hypothetical year production figure say even with bulk ordering from a supplier contractor a u jointed shaft was lets say $5 each part to GM as a bulk purchase for their assembly line, however the rag joint is costing them lets say $1 each. The rag joints would cost $350,000 or $1 per truck. The u jointed shaft would cost them $1,750,000 @ $5 each per truck. They both do an adequate job for the average joe. Most people could give 2 ***** if GM used a u jointed steering shaft in their trucks or not.
This higher cost part adds to the window sticker of the truck, and if not added onto the cost of the truck would be felt by company shareholders, so the customer pays with a mark up to lets say $8 more being added to the window sticker. Keep in mind this is only one cost cutting example. And if they did that with enough different parts on the truck, the customer, who shops by price, would buy elsewhere.
Is a rag joint the "best" solution ? No it isnt, however its by far the cheapest from a bean counter standpoint, and worked "good enough" for 99% of the people who bought these trucks brand new concidering the fact that they would be hitting the wrecking yards either wrecked, rotted out, beat to ****, or just plain worn out by the 15 year mark.
Why do you think the 90° 4.3 V6, 305s, and 350s in these trucks are all SAE thread, when the cabs and chassis are metric? It sure as **** isnt out of tradition, though we would like to think so. Its because the same tooling and processes thats been making small block V8s since 1955 was probably still being used to make the engines in these trucks in the 80s and 90s. Why spend money to retool for metric hardware on the engine. Costs more money with no additional benefit.
I am in the process of restoring 2 second gen plymouth barracudas. One is a 1967 sport coupe 1st year second gen. The other is a 1969 sport coupe last year of second gen. What the manufacturer cheapened up between 67 and 69 is pretty epic even though they look pretty close to the same. Stuff was done for cost cutting. By really looking at the differences in everything between both cars you could imagine the beanies at work telling the stylists and engineers to make it cheaper, sell it same price etc.
Personally i am glad jeep being the 4th largest automaker, used saginaw steering boxes specced with GM splines and went with a U joint setup. This makes it easy. As a smaller volume manufacturer with a reputation for trucks that are like billy goats for their agility and climbing ability in offroad situations, that u jointed shaft was concidered a necessity, and worth it to them to have it add to their bottom line.
Sorry this is long winded, however In closing, yes they both work and do the job, the u jointed shaft has a more positive feel, and is a way better quality piece. Install it and its done. You could hand the truck down to your grandkid one day, and they would prob never have to replace it either. Rag joints were only used because they were cheap to produce and worked ok for most people. It was only done that way to keep costs down.