analysis shows that once one side uses nuclear weapons in Europe the balloon goes up and its all over.
You are describing the policy of Tripwire - which was replaced by Flexible Response because it wasn’t credible. Which is precisely why tactical and INF weapons were developed - to ensure that escalating chain of use.
The idea of tripwire is that any attack by an enemy would invoke a full scale strategic response.
Which raises the question, would the UK, as an example, risk its existence, and it’s deterrent, to save Krakow? If not, when the threshold be reached?
Which raised the probability it never would - which invited the possibility of an attack by an enemy who made their decisions on that basis.
Flexible Response put nukes into the hands of battlefield commanders - if an Honest John was used, would the next step be a Pershing and so on up the ladder - suddenly the risks of escalation and the invocation of the strategic forces becomes a real risk - so no one would risk the first step.
The INF Treaty removed all such weapons meaning any future war would just be conventional and not risk the use of the strategic forces on either side, and each side knew they could defeat a conventional attack.
The reintroduction of sub-strategic nuclear weapons by either side unbalances that calculation - and the fear that the side with the weapons might use them without fear of retribution because of the calculations above.
https://publications.parliament.uk/p...25/225we17.htm