"Technology (satellites, computer, ML) has come a long way during this time"
That may be true, but there's so much you can take with you! These modern rockets are nowhere close to the lifting capacity the Americans used. Which means you can't do the landing, stabilizing with so much brute force to keep your vehicle steady. The less weight is available to you, the less energy you can take with you. The less stabilizing you can do using sheer force, the more precise you have to control your landing. The more complicated routines needed, the more measurement and sensor technology to install. The more complex the programming, the more complex your systems, both hard- and software. The more complexity, the more can go wrong, etc.
Engineering with "unlimited" resources allowing you "a lot of energy" and "a lot of weight" allows the engineer to use more "raw" and "basic" solutions which is not comparable with high-tech engineering if you have only limited resources and limited power and limited weight-fuel.
To visualize this for those among you who are no engineers:
Imagine you have a water reservoir and the only task for the engineer and later operator is to either lock the reservoir or open it to drain the levels.
You basically just need one big switch: open or close.
Not much can go wrong there.
But now you add more tasks (only tasks to open up more or less without really interfering each other):
- Opening % based on demand of farmers needs down the river
- Open % based on demand of power production
- Open % based on demand for fresh water down the river
And now you're going to add more tasks that actually interfere with each other:
opening up more for farmers' needs, but the turbines produce more energy into the power grid, the energy into the power grid is based on voltage, current, and frequency, more water = higher frequency (a standard defines the boundaries between which frequencies it can variate). You're now getting to the maximum of that boundary, but farmers still need more water, so you have got to either limit the turbines or reroute water through different flows.
See what is going on here? The more complexity, the more switches needed, the more the engineer and operator have to consider.
And now I'm going to tell the engineer and operator additional tasks:
The original design the switch controlled a 1 meter radius water flow pipe with 1.5 cm stainless steel. But in the new design the engineer should limit the pipe to 0.3 meter and the thickness of the pipe to 0.4 cm and please below 350 kg per meter pipe. So steel is now out of the question, getting more complicated.
Also just opening one pipe for the operator might not do the trick. You need to handle a multitude of switches even for the same task based on the limits of weight, available flow, etc.
See how complex it is getting already with such an extreme simple comparison?
So just because the USA could do it with old technology and their extreme heavy lifting capacity doesn't mean you can copy it or do it easier just because you have more technology at hand, if at the same time you're going to do it with a lot more restrictions than US engineers had.
And the lifting weight for any space operation is the absolute most daunting restriction for any engineer in that field.