"it was under-powered and weakly armed when compared to its contemporaries.Most critically, it was out-performed by the Messerschmitt Bf 109E during the Battle of France."
The French Morane-Saulnier M.S.406 fighter interceptor. Found during the Battle of France  to be less than adequate, deficient when compared to the German counter-part.
But that is not the end of the story.
That M.S. 406 when modified and improved upon by the Finnish Air Force [FAF], a much better warplane, used successfully by the Finns in combat with Soviet forces, IN A MANNER AS WAS ALSO THE CASE WITH THE AMERICAN BREWSTER BUFFALO! The Finnish designation for the M.S. 406 was the Mörkö-Morane!
Improvements and modifications, not that so excessive and extensive but enough to create an almost new war-bird with significant potentiality. And when used and flown by outstanding Finnish combat aviators in a way to maximize strengths while minimizing weakness, deemed more than sufficient!
Improvements and modifications to include but not totally limited to:
* New and more powerful engine.
* Improved aerodynamics.
* Improved and strengthened armaments.
"The aircraft designer Aarne Lakomaa turned the obsolete 'M-S' into a first rate fighter,"
"The first example of the modified fighter, MS-631, made its first flight on 25 January 1943, and the results were startling: the aircraft was 40 km/h (25 mph) faster than the original French version, and the service ceiling was increased from 10,000 to 12,000 m (32,800 to 39,360 ft)."
And again, when flown by determined and able Finnish combat pilots, impressive with the "kill-ratio"!
"Between November 1939 and 4 September 1944, Lv28 [FAF combat unit] scored 118 aerial victories flying the Morane M.S.406 . . . The unit lost 15 aircraft."
What is it about the Finns that allows them to excel as they do? Think modern Finland, a small nation [about 4 million persons tops] but with superior educational facilities and top-notch students, Nokia, Linux, superior and innovative designs, etc.
Think too of the Israeli and the American F-4 Phantom. That Israeli making no less than five hundred  changes to the basic F-4 upon arrival.
The Finn during the Second World War [WW2] comporting themselves with honor, John Keegan rating the Finn as the BEST soldier during that conflict. Apparently the ground troops and airmen both!