I do love that line, but I also have to admit that Olivier could be super hammy (I love Sleuth, but he hams it up like crazy) and Brett is Holmes. Similarly- Daniel Day-Lewis gets into his roles to a ridiculous extent, living as if he were the character for months, which is going much further than Brett, but it’s really paid off for him.
Really, I don’t think there’s one way of being an actor. If you’re a quick-change artist and you can put on a convincing performance, terrific. If you need to study your part like you were writing a doctoral thesis to put on a convincing performance, also terrific. Olivier got a lifetime achievement Oscar and his own award named after him. Daniel Day-Lewis has won three Oscars. Obviously, both techniques work out, but Olivier’s sure seems less taxing.