D the G. Operation sealion required 4 conditions to be met before taking place.1)The RAF was to be "beaten down in its morale and in fact, that it can no longer display any appreciable aggressive force in opposition to the German crossing". That is documented fact.
As Teribus states the bi plane Gloster Gladiator was the immediate predecessor of the Hurricane and first in squadron service on 23 February 1937. It was obsolete before it entered service and superceded just over a year later. Even the RAF described it as "an anachronistic survival from an earlier generation of fighter aircraft. The Gladiator filled a gap in defence requirements between the older biplanes and the new, modern monoplanes"
Had the battle of Britain been fought with an inferior aircraft the outcome would have been very different and the first qualification for sea lion to occur would have been satisfied.
Some of the above may be regarded as conjecture but no more so than holding your hand in a flame and disputing as to whether or not you will be burnt.