Is it normal for a corrected undescended testicle to be much smaller than the other?

Yes: There is usually something wrong in the undescended testicle, related to why it did not descend. It may be smaller, and only partly functional. It also has a higher chance of becoming cancerous. So, if previously undescended testicle is small, and then grows rapidly to match the size of the normal testicle, the "undescended" one may have a tumor in it . . . And a doctor can evaluate for cancer.

Often yes.: Firstly undescended testis (ut) may have been smaller than the normally descended before it was brought down. Secondarily, delicate blood supply to the ut may have been slightly compromised during surgery. Good thing is that the ut is now down. There is only avery small chance of future malignancy, however the previously ut, now can easily be palpated so you'll discover any change early +get help.

No: It isn't normal for a corrected undescended testicle to be much smaller than the other. It may be slightly smaller, and this is usually due to the fact that the testicle was abnormal to start with. If the testicle is much smaller, it usually is an indication of inadequate blood supply of previous torsion with partial resorption. Physiologic function of this testicle would be questionable.