You should realize that by 2241 Enclave was only^ in Oil Rig (around 1 thousand peole)^^ and in Navarro (not more than 100).
Then during sabotage in Oil Rig some (obviously not more than 1/2 looking positively or rather 1/3 looking truly) escaped, and those we see in F3 in Raven Rock and around Capital Wasteland. Then Raven Rock, Mobile Base Crawler and Satellite Relay Station are destroyed, not even mentioning all outposts in Capital Wasteland, each having few members, which are lost too...
There are around 35 outposts + and 18 Vertibird events, so 53 in total. Multiply this by 3 (average number of Enclave soldiers per place) and we got 159. Take casualties from destroyed bases, and well... Enclave is basically lost, without any chance.
^Richardson dialogue
^^Curling dialogue