Exactly! Shin Buu and Fat Buu are restrained while Chibi Buu isn't. The quote refers to power and evil, not only evil.
No, when they talk about Kid Buu having no restraints they mean he has no goodness in him to hold him back. NOT to hold back his power but to hold back his actions. Notice what he did as soon as he emerged. He blew up the planet just for kicks, not caring about anything else. None of the other Buus did this. Fat Buu was just playing and Super Buu just wanted to challange himself. Kid Buu just wants to break stuff.
And again, it isn't stated that only Dai Kaioshin weakened Buu since there isn't plural in Japanese.
If you use that logic then it's also not stated they're referring to both.
However, it is implied they're referring only to the Dai Kaioshin.
Wrath Buu is still restricted by Kaioshin. You can see that by his clothes.
Evil Buu is pure evil, there is no Kaioshin influence in him at all.
You said yourself, you can't say definitely each one or both they are talking about, yet you concluded they're talking about Dai Kaioshin.
And you concluded they're not, even though it's implied they are.
Since they don't specify each Kaioshin is safe to assume they're talking about both absorbed by Buu.
Actually, its safe to assume they meant the one they directly referrenced. Considering that 1) no comment was made about Buu's power dropping after absorbing the South Kaioshin and 2) Super Buu's power increased when he became Buff Buu it's 99% certain that
only the Dai Kaioshin weakened him.