I'll adjust my phrasing.

As a user, building with thin-lto vs full-lto generally produces pretty similar performance in no small part because a huge amount of effort has gone into making the summaries as effective as possible for key performance needs.

As a compiler developer, especially when developing static analysis warnings rather than optimization passes, the number of cases where I've run into "this would be viable if we had full-lto" has been pretty high.