This season we've had 5 distance races before Tour de Ski, neither of them were in any way comparable with that 15k in Toblach. Even the skating mass start in Ruka were a lot more selective where only a couple of athletes were able to catch up the gaps created in the climbs. Looking at rest of the season it doesnt look to be many races where one can expect similar to what happened in Toblach on that stage 2.
It's also a bit hard to define that 1/3 of the races should be for the pure distance skiers, because some of the all rounders like Diggins are better distance skiers than some of the "pure distance skiers".
About 1/3 of the races are sprint races. The rest 2/3 is races where skiers like Johaug, Weng, Andersson etc are competitive or favorites. These are light weight (more or less pure) distance skiers. There are plenty of chances for these type of skiers. Sometimes they are being served the chance on the plate (like Alpe Cermis and in Lillehammer), other times they have to fight a bit for it (like in Ruka). I dont think the balance is bad at all.
I personally also am much in favour of distance races (preferably interval starts) and have been thinking since the first Tour that a pure distance skiing Tour would be more interesting. But the target from FIS with the Tour has been to award the most complete athlete (whatever the F that is) and I dont think there is anything that points in the direction of sprinters being so much awarded from the sprint races that they end up at the top of the GC.
From the 18 Tour de Skis we've seen I think on the womens side it's only 4 times (out of 54) an athlete mostly seen as a sprinter has ever podiumed the overall. Two times Follis, one time Majdic and one time Stina Nilsson. And these girls were also pretty solid distance skiers. Follis won Olympic bronze in skiathlon, Nilsson Olympic bronze in 30 km and Majdic won the World Cup 30 km in Trondheim (the year they rebuildt Holmenkollen) solo.
On the mens side there isnt really a single guy that have podiumed that have been more of a sprinter type when looking away from Klæbo. The only other candidates are Krogh (but he's also a Skiathlon World Championship medalist and won and podiumed several 10/15 km interval starts) and Østensen (he had a strange career, but looking at his results in the Norwegian Championships and Scandinavian Cup he was a better distance skier than sprinter, but struggled with a lot of bad luck with health and sometimes also unfair selections).
I think the problem with the sprints are that it's impossible to know exactly how much it costs to do all heats compared with the ones doing less or none heats. But 3 extra heat, with the warm up and full process costs a lot, so I dont think the bonus seconds are completely out of touch. And with "only" two sprints, Alpe Cermis is balancing well and as we've seen over the last 18 years, basically everyone that ends up on the podium or even top 5 are skiers that are winning distance medals at World Champs and Olympics (or regularly podiums in the World Cup).
Looking at their career Randall podiumed 29 World Cup races and won 2 individual Championship medals and Steira podiumed 22 World cup races and won 5 individual Championship medals, so basically it wasn't any huge difference between them. And the calendar hasnt changed that much since they competed. Steira in her peak wouldve definetively been fighting for a podium in Ruka 20 km, both distance races in Lillehammer, Davos 20 km, Val di Fiemme today, Alpe Cermis tomorrow, the mass starts in Les Rousses, Engadin and Falun. Both distance races in Oslo and the 50 km in Lahti. And of course the two longest races in the World Champs. Randall podiumed 1 classic sprint in her career, so one could almost argue that she would only have 6 World Cup races + the World Championship sprint.
I would like to see where Siebenthal said that was the reason to retire., because from what I can remember she didnt publically say that as a reason at all. She took a break from training in the spring and summer after 2019 season and then she started training again in the autumn with the target to continuing her career, but when she started training again her body and her head was resisting. This is what she said when she announced the retirement, for example to
SRF.
Also with the Johaug argument (Johaug won 11 races in World Cup and World Champs the last season of Von Siebenthal, even with skipping the Tour) you basically confirms there were plenty of races that suited the type of skier that was Von Siebenthal... If Von Siebenthal lacked chances, it's mostly because she lacked a lot of ability in classic. If it was like you described that all the races that suited her was won by Johaug, then the problem was Siebenthal wasnt good enough, not that the races didnt suit her. But I think it's pretty obvious that you are wrong about Von Siebenthals reasons for retiring.
I agree with the whole things with relays being suboptimal from both FIS and many national team, but I dont have any clear solutions or answers here.