Is the story of Abdullah ibn Mas'ud with those who glorified God with pebbles considered evidence against the impermissibility of excessive devotion and exaggeration in glorifying God (tasbih) and seeking forgiveness (istighfar), or is what this person does correct?

If a man's chanting of adhkar (remembrances of God) and du'at (supplications) leads to an exaggerated prolongation and melodic ornamentation resembling blameworthy tunes, then it is makruh (disliked). This is because the desired outcome is humility and contemplation, and performing them with tunes that resemble those of the dissolute deviates them from their true meaning. Scholars have disliked reciting the Quran with such tunes, and the same applies to all other adhkar and du'at. However, improving one's voice when reciting adhkar and du'at without melodic ornamentation is permissible, especially if it aids in contemplation and humility.