Britain declared war on Germany in 1939 because they could not continue the pace of rearmament without emergency powers...that was 1939..how they supposed to continue rearmament through 1942 without emergency powers to finance all this?
likewise the malaise that afflicted the French took decades to take root, it could not be reversed in a matter of years. Likewise the damage to the Soviet Moral from purges and decades of abuse could not be overcome in a matter of years....it would take a decade or more.
Without knowing about the British situation, although that sounds like nonsense, the French situation and economic malaise came about due to specific situations in the 1930s which the French were due to their political and economic situation poorly equipped to respond to - although their decline in the initial period of the Great Depression was less than other nations. French politics had produced a stalemate situation which made direction action about economic matters à la New Deal and the like difficult, while the solution which proved the way for the British out, easy monetary policy and devaluation, was off-limits politically due to the fallout of the 1927 French devaluation which had undermined confidence in government. The French bourgeois were unwilling to accept another devaluation, but the Popular Front brought one through in 1936, and further deflations would follow this. The un-competitive nature of the French economy had been fixed as a result, and the French industrial index had surpassed the 1929 one by 1939, with growth continuing. With the world economics situation emerging out of the depression, the French economy will be able to assume its regular role throughout much of the 19th and early 20th century; unremarkable but steady growth. People generally contrast this negatively to other nations, but French economic growth in GDP per capita largely kept up with their European competitors, the main difference was that their European competitors were also growing quickly in population which made their GDP growth look much more impressive.
Furthermore, while the problems that led to the 1930s were a long-time in coming, it must also be added that French economic performance was not always poor in the first part of the 20th century; the 1920s were a period of excellent economic growth in France which had seen the French economy outpace the German economy in economic growth.
Of course, it is impossible for the French economy to challenge their German equivalents in economic sizes, as the Germans had grown to around twice the French population and had control over an economy, which due to resource alignment, was naturally more capable of supporting heavy industry. But the French economy was looking up in the late 1930s, and while there were as always worries about the debts from re-armament, they were absolutely nothing compared to the disastrous situation across the border. And unlike Germany, France still has the largest gold reserves in the world to finance its re-armament...
Additionally, while the French economy had problems that were structural, such as its dependence on small peasant cultivators for agriculture, the German economy was largely the same.
Similarly concerning the Soviets, the Soviets don't need to perfectly heal all of the problems that the purges brought, they just need to recover to a sufficient extent to outdo their 1941 baseline. This is not terribly difficult, and by 1942, under peace-time conditions, the Soviet Union would be far on its way to dealing with this. Another large reason for Soviet failures in 1941 was Soviet logistics, but these would be much better for supplying their forces in most any other hypothetical war with the Nazis.