(good, better, best) are irregular adjective spellings; good (adjective), good in the Comparative means (better) and means (best) in Superlative.
Adjective-good, Comparative-better, Superlative-best
Normal form of adjective tells 'what-kind-of': has to agree in gender and number in spanish spellings: singular, bueno, -os (buena, -as, f.) good (ending agrees in gender/number in spanish.
Comparative spanish adjective form is irregular, spelled totally different: mejor= (better), plural-mejores
Superlative adjective form is specified adding the article for 'the' : el, m./la, f. mejor (the best)l plural, los/las mejores
Apparently the definite article in this Spanish idiom specifies the distinction between the comparative and superlative. So the fact that the "el" is present means that "best" and not "better" is intended. In fact, it's the very difference between how you say "better" and "best."
Who knew? Well, me, now, after getting this one wrong.
"I am better" could apply to health.
"How are you feeling today?" "I am better."
In this statement the comparison is assumed. The understood comparison is between today and yesterday.
However, none of this applies to the current problem for which the only correct answer is, "I am the best." Here there also exists an understood comparison, and that is between the self and everyone else.
Yep, though to be clear, the definite article makes the difference between the comparative and the superlative. So "mejor" by itself means "better." "El mejor" means "the best" or "the better" (correct in English for comparison of just two things, though out of fashion in my experience except in idioms like "the better man").