Your arguments make sense, so it appears that continuously-welded rails should be better than the traditional jointed rails.
Nevertheless, when I was young I traveled frequently by train. During some decades, I have never seen problems caused to the train traffic by too high temperatures, on traditional jointed rails.
On the other hand, in the last few years, whenever I happened to travel by train through Germany on continuously-welded rails and the weather was hot, there were train delays due to the rails.
So it seems that there is some disconnection between theory and practice. Maybe the new continuously-welded rails have been designed based on ancient recorded temperature ranges that are no longer valid due to climate changes, as already suggested in the parent article, but in any case something is wrong with the design of modern rails.
In the parent article it is mentioned that changing the stress-free temperature to a higher value is not good enough, because the strength of the rails could be exceeded during cold winters. So it is likely that the rails would have to also be thicker, increasing their cost.
> In fact, jointed track is at a MUCH HIGHER risk of buckling in heat than welded rails as gaps close and there are 160+ joints PER MILE to maintain...
Why? Don't the gaps give the track some amount of play which would lower the pressure and therefore the risk of buckling?
I don't have a reliable source, but I recall hearing that expansion gaps require the rails to have some freedom to slide back-and-forth, as the expansion and contraction occurs over the whole length. The rails are not guaranteed to go back to where they started when they cool down, so gaps can close up (while correspondingly widening elsewhere to compensate), and if you have too many closed gaps in a row, the rails can jam.
The rails have not a real freedom to slide, they have two different forms of resistance, the one provided by the ties and the one provided by the junction, there is only a given temperature range where they can slide.
The rail goes into a cycle, you need some 3-4 C° to win the resistance of the joint (in this part the rail is compressed by some 6000 kg of resistance) and some 6-7 degrees more to win the resistance of the ties (some 10-12000 kg more of compression), then it becomes "free sliding" until the gap in the joint closes, this needs 12-13 C° more and the rail is again compressed by the ends.
When the temperatures lowers, the same cycle is reversed, the rail first contracts until the gap starts to appear and widens, then you have again a range where it is free sliding, then the two resistances come into play again, when the temperature lowers further the excursion is limited by the joints (usually they allow 14 mm travel) and the rail is subject to traction (as opposed to compression).
The only point that never moves is the tie at the center of the rail length, you have to imagine a spring that you try to expand by pulling the two sides, it will return to its original shape, all forces are relative to the center, so there is not any reason why the rail should not come back to its original position.
The gaps do give some amount of play. The trouble is that once the temperature exceeds the design maximum the gaps close up completely and all that expansion force is directed into hard metal-on-metal contact, at which point something has to give. Jointed rail tracks are not designed to handle those forces without buckling because the whole point of having the joints is so that they don't have to.
It is worth pointing out that jointed rather than welded track WILL NOT solve the buckling problem.
In fact, jointed track is at a MUCH HIGHER risk of buckling in heat than welded rails as gaps close and there are 160+ joints PER MILE to maintain...
...plus jointed track is generally lighter, weaker and thus at higher risk of buckling (most GB buckles are in jointed, not welded track).
Bolted joints also have a nasty habit of disintegrating under traffic and derailing trains (hence use of welded track to start with)