I took some time to review something that was "authoritative" from 50 years ago, and yes, the carry-over to the modern times is not great. Does it make me weak to question it ?

I am purposefully not "self-assured" but rather, looking into the topic. As a learner, why would I not question the contents I found?

The textbook leaves no room for alternative -- in fact, the tone and presentation of the textbook is that the topic is settled, and the math is "best".

That's the nature of a textbook though, not the field.

Most textbooks present a pretty definitive take on a topic, if only for pedagogical reasons. You might get a few well-defined controversies, like various theories of matter in chemistry, or frequentist vs. Bayesians in a stats book. Even there though, that debate is often resolved, one way or the other, by the end of the first chapter.

The actual back-and-forth in most fields happens in journal articles and conference presentations instead.

Having formerly been a medical scientist, i don't entirely trust medical scientists to get this stuff right. But currently being a computer programmer, i really, really don't trust computer programmers to get this stuff right.