I send text messages to others and they reply to me, oh, thank you. Isn’t it a bit perfunctory?

Not all, it depends on the relationship between the person sending you the message and you. If it is a boyfriend and girlfriend, it will be a bit perfunctory. If it is a good friend, it will be a bit perfunctory. If it is an ordinary friend, it will be a bit perfunctory. You are more polite. Most of the people who reply "Oh" now are speechless, so don't think too much.

I hope you will adopt it, thank you!