It’s not that a dub can’t be good, but I don’t understand how you can know if a dub is accurate. You would need to have the dub and the original side by side and watch line by line to see if it fits right? With a sub you have this automatically. Of course due to grammar it can be the next or previous line but generally you can listen to the original and read the sub at the same time to check for differences. I don’t do this consciously but it is effective.

One time I was watching one of my favorites and an emotional scene came up. However the sub was not accurate and diminished the emotional impact. Luckily it was not a hard line and I could just hear the Japanese which saved it for me. If that happens with a dub, you wouldn’t know. That is my problem with dubs, not if the voice acting is good or not. I’m sure there are many good voice actors in other languages that do a great job.