After that he spent a whopping 437 days on Mir (which had about 1/3rd the pressurized volume of the already claustrophobic ISS) to see how the human body would respond to long-term duration in minimal gravity. Upon landing back on Earth this time he decided to get up and walk from the capsule to his rest point (astronauts are normally carried/rehabbed due to muscular atrophy + dysfunctional balance/orientation, even for far shorter stays), making a point of the fact that he was just fine. Dude was just a complete badass. The USSR would have beaten us to Mars if they hadn't collapsed in 1991.
In any case, it's probably a good idea to do a flyby because there will be with, near 100% certainty something things we hadn't considered and others that we simply were not aware of. By first doing a flyby and then a landing you increase the chances of success. And the people doing the flyby will probably be mostly the same people doing a landing a couple of years later - so it'll be more like "See you soon."
[1] - https://en.wikipedia.org/wiki/Valeri_Polyakov#Cosmonaut_care...
The only fundamental tech we're missing is a heavier launch vessel, which we've already developed in the past - and have actively in development in the present via Starship. China is also developing their own super heavy vessels. But these developments taking 8 years is quite conservative. We went from practically nothing in 1962 (having only just put a man into orbit, and barely at that) when Kennedy gave his to the Moon speech. 7 years later in 1969 - we'd be landing on the Moon. And that landing posed far greater difficulties than just an extended flight, let alone when they were building from nothing, and we have all of this knowledge and prior experience to build from.