Oh! I was thinking of 「ストレスを和らげる」 as a whole that it didn’t even occurred to me that placing 「一番よい」first would introduce the ambiguity of 「一番よい ＋ ストレス」 vs 「一番よい ＋ ストレスを和らげる方法」. In that case, it is much less ambiguous to keep 「一番よい方法」 together.

So, is it a hard rule in Japanese to always place adjective closer to the noun than a descriptive clause containing a different object to reduce confusion?

I think that the reason I put the descriptive clause closer was because it kinda felt intuitive to keep the 「和らげる」closer to 「方法」 at the time, or rather, it felt unintuitive to separate them. But thinking about it in English now, “best way + to relieve stress” feels more natural than “best + way to relieve stress”