All along, Japanese "ぁぁ" can only be pronounced as "A" and "ai" under any circumstances, right?

Neither pronunciation is accurate.

Like English and Russian, Japanese has the phenomenon of vowel linking. However, when I sound is pronounced in English or е sound is pronounced in Russian, one is often dominant and the other is auxiliary, while when ぁぃ sound is pronounced in Japanese, the length and weight of ぁ and ぃ are basically the same.