No. In Jain Dharma, having deep devotion to one Tirthankar does not mean you are doing ashadhana toward other Tirthankar Bhagwans.

All Tirthankars are equally revered as Vitrag, Sarvagna, and Kevali. If your heart naturally feels special devotion toward one Tirthankar, that is bhakti—not disrespect to others.

What matters is this:

• Respect all Tirthankars equally
• Do not compare them with bias or contempt
• Do not think one Tirthankar is “greater” and others are less
• Keep devotion pure, humble, and free from sectarian pride

In Jain understanding, a “favourite” Tirthankar can be your isht dev for personal devotion, but your reverence should remain for all 24 Tirthankars.

So, if your devotion to one Tirthankar increases your faith in Jain Dharma and strengthens your samyak darshan, it is good. It becomes ashadhana only if it leads to:

• disrespect for other Tirthankars,
• narrow-mindedness,
• or denial of their equal spiritual perfection.

In short: Strong devotion to one is fine; disrespect toward others is not.

If you want, I can also explain this from the perspective of samyak darshan and bhakti in Jainism.