Let me begin first.
The quality of Hindi dubbing for South Indian and Hollywood movies is getting worse. This happens because they rush to finish the work quickly and don't have enough money. So, they hire inexperienced people. Also, there's not enough checking to make sure it sounds good. To fix this, they should hire skilled people, spend enough money, and make sure the work is done properly.
It's not always their fault. Sometimes, the acquisition rights for a big actor's film are so high. Thus making it difficult for the Dubbing Companies to complete the project with certain budget.
If they stick to certain rules and use technology wisely, they can make the Hindi dubbing way better for everyone watching.
(Exceptions are always there.)