The first novel establishes Sandokan as firepower-heavy and technologically more sophisticated than other Indian Ocean pirates and warlords of the mid-nineteenth century, with every following novel increasing his band technological sophistication and firepower-per-capita. At first it seems strange, especially considering he can kill a tiger with a knife and his arms can break up manacles with no effort, but his Origin Story has him experiencing first hand that all his strength and courage are worthless against a bunch of guys with flintlocks, and that very novel had him trying to board a Royal Navy warship and utterly fail when said warship used her steam propulsion to keep distance from his flotilla of sail-powered prahos. Of course he's going to use as much firepower and technology as he can: he knows first-hand that firepower and smartly-used technology trump valour nine times out of ten, and is trying to even the odds against the British and become invincible against anyone else.
Lord Guillonk goes from respecting and even liking Sandokan when he doesn't know who he is to sudden loathing as soon as he's informed of his identity in spite of knowing he's a respectable and even nice guy, and then back to liking after he saves his other niece Ada and cures her madness. This is easily explained by the fact he's a retired Royal Navy officer who first came in the Indian Ocean to fight pirates with his own private crew and ship: he came to the Indian Ocean with a low opinion of pirates (by British and international law, "enemies of the human race") and saw first-hand what the pirates (especially those who are Dayak head-hunters) would do to their victims, and suddenly discovering that the Brunei prince he let in his home is actually a pirate with a horrible (if exaggerated) fame is bound to cause a bad reaction; in the same way, suddenly discovering that not only his supposedly dead niece Ada is alive but Sandokan went to near-certain death for her sake and that of her fiancee ran completely opposite to that opinion, and he could not deny the facts.
The fake Meccan Pilgrim in "The King of the Sea" bragged that no torture could break him, yet it didn't take long for the Americans to do just that with the water cure. Thing is, the water cure is an European torture that nobody had used in the Indian Ocean for centuries, so he had no idea of it. As for how the American crew knew it well before the US Army learned it from the Filipinos (who learned it from the Spaniards), they're sailors and could have seen it done by Spanish troops in the Filipines.
