When I answered the question, I looked at it from the standpoint of the average person today. Let's take a typical mother of two, full time job, no cleaning lady. She vacuums at least once every two days, with daily 'tidying up' of the living room. The convertible has terrible suction through the hose, so it wouldn't do well on her sofa. The modern person wants the tools on board, not in the closet. As always, she will want the vacuum to clean FAST. She doesn't want to deal with broken belts (because the convertible belts are in the middle of the path of dirt). She doesn't want to 'watch out for' pennies, rocks, etc. which cause fan breakage. She definitely wants HEPA bags (although MOST people today don't want bags at all). It's not really true to say that modern plastic vacuums last a short time - remember we all said Hoover Elites were JUNK and wouldn't last, yet many are now 20 years old. The Windtunnel launched in 1995, almost 20 years ago. Most are still running, or could easily be repaired. Belts and brush rollers are still available for Windtunnels, and will be for some time to come. Convertibles are done and over with. Yesterday's cleaner. If it was New, on the shelf today, no one would buy it. I cannot see a busy modern consumer buying it. It doesn't fit in with their lives any longer, just as the wonderful Hoover 28 didn't fit into the life of the consumer who bought a new Model 65 in 1958.
So from the standpoint of Cleaning The Home, the Windtunnel would certainly clean easier, faster, and 'better' in that the customer would use it far more often and be much more satisfied.
From the standpoint of an enthusiast, well, that's a different story. I prefer vintage canister vacuums to anything modern, again, as an enthusiast.