Sorry to be pedantic, but the Baltimore, Maryland and Hudson are all American aircraft flown by the RAF & Coastal command under lend-lease, although I would like to see them all in the game.
The Defiant had a quite short career during WWII- was active in '39-'40 as a day fighter and flew many sorties around the time of Dunkirk and very early part of BoB, but was a sitting duck once the Luftwaffe worked out it had no forward firing armament, and was restricted to early night-fighting, where it had some success, but with its low top speed and lack of radar it was soon superceded by the Beaufighter. I agree it is a good looking aircraft, and is a fine example of British 'quirkyness' in design, but the single engine turret fighter always struggled with performance because of the extra weight (the Roc is another example) and was a dead end design.
The Wellesley was an obsolete design by the outbreak of the war, and none fought in Europe (there were only four in the UK at the outbreak of war). A few did fly missions against Italian forces in East Africa, flying their last combat mission in November '41. It was important from a design point of view, as it was the first aircraft to use Barnes Wallaces 'geodesic' construction method, but an aircraft of its size powered only by one Pegasus XII was never going to stand up well to fighter opposition, many being lost to Italian Cr42's (!) in Ethiopia.
The Lysander and Whitley had long and successful careers, both flying throughout the war- the Whitley being a front line 'heavy' bomber until the four engined designs made their appearence, then being a transport, paratroop carrier and flying with Coastal Command. The Lysander was initially an Army communications aircraft but found its most famous role delivering and collecting Allied agents in occupied France. Both deserve a place in IL2.
The Blackburn Roc, again, had a very short and limited career, and the Whirlwind was cursed with the unreliable Rolls Royce Peregrine's which hampered its career. Only 2 squadrons operated the Whirlwind in combat (263 & 137) with the last operational sortie being flown by 137 Sqn on 21st June '43.Both squadrons re-equipped with Typhoons and the Whirlwind was declared officially obsolete on 1st Jan '44- after the first squadron to become operational was in December 1940, thats an operational life span of just 2 1/2 years! If it had been fitted with better engines (Merlins?) it may have been a far more usable aircraft, especially with its 4 nose mounted 20mm cannon- you can guess that it probably would have been fitted with rockets later in the war had it survived, which would have made it a seriously handy ground attack aircraft, but as it was, it really didnt play a big part in the air war.
For my money, I would say the Beaufort and the Stirling are much more important aircraft than the Roc, the Wellesley and the Whirlwind as far as their parts played during WWII- Stirlings were front line heavys, then transport, glider tugs and paratroop carriers and the Beauforts were active in every theatre that British forces fought in, from Coastal Command and the RAF in the Atlantic and Biscay, to the Med and Malta, to the Far East.