Welcome aboard Spikes!
You pribably think that your question is simple resulting in a simple answer, unfortunately we might see weeks of discussion instead.
The first thing to realize is that there is no perfect machine design, they all have trade offs. The one big advantage under the table linear systems have is protection of the leadscrew and bearings. To some extent anyways as does gets everywhere.
Im not familiar with the designs and being on a cell phone at the moment wont be looking them up. In any event the number one consideration in my mind is that suppirted rails are used, if not the design is not stiff enough to consider. So if we are past that the next question is how far apart are the bearing blocks? Twist is a functionplay in the bearings and the stiffness of the rail and bearing block assembly. The fartger apart you can separate the bearings the less of a problem twisting becomes. Of course this creates an issue where you have a lot of dead space on the table where the gantry cant reach.
Now some people obsess over that dead space, having worked a bit with turret mills im not bothered. In the end you figure ot the work space you need and size the machine accordingly. Im pretty sure one could go thriugh the mechanical engineering to figure out what an acceptable bearing spread would be for the size of machine you are interested in. Before even doing that though you need to nail down work area size and what you can accept for over all machine dimensions. In any event it isnt impossible to get a working machine, that gives acceptable results, with a leadscrew running down the center. It depends upon many factors but the ratio if table lenghth to width can have a big impact on viability.
In any event lets say that you have a large table that would benefit from dual leadscrews. Driving them from a single belt can certainly work but again it is the details that matter. How far apart are the leadscrews, the belts type, belt support solutions, even belt width are factores. So yes it can work and actually work well if carefully engineered. The gotcha is that the belt will need to be tensioned tight and thatdoes require stiffness in that area of the machine.
In any event if you look at alternative designs for large table machines you almost universally see dual leadscrews in part because the bearings are on top or the side. The problem with many designs in my opinion is that the X bearings are too close together supporting really narrow columns holding up the Y axis. So you still have an area for twisting to happen though it might be more of a rocking. It comes back to guys wanting the machine to be as short as possible. As long as they understand they are trading off stiffness for machine length there isnt sn issue. However if their goal is be best possible accuracy and solid alignment it doesnt make a lot of sense to me.
Now there us a huge number of qualifications here the rail type (round or profile, its size the bearing block preload, the machines construction materials and etc all come into play. If you want a machine with under the table linear motion components id say go for it understanding the trade offs. If you consider all the issues and you dont want to address them consider another design. In the long run dual lead screws and the required steppers isnt as damaging to the budget as some alternatives. For instance for a single motir drive dual lead screws drive yiu will need to buy suitable pulleys, belts and iflers at a minmum. One of those pulleys will need to allow for phase adjustment or the leadscrew bearing block will need to be adjustable for position ( for final gantry square up). Also this axis "MAY" require a bigger stepper if only one is driving.
I expect you will get a lit of opinion expressed in this thread but in the end a viable build is all about engineering and build quality.