Wordsmith gives an excellent example of a tragic tendency
of English to take a fine complimentary word, and let the
meaning drift to a snotty sneer. Der Quibblemeister is
shedding great big tears.

sententious (sen-TEN-shuhs) adjective

1. Full of pithy expressions.

2. Full of pompous moralizing.

Even if the drift you are speaking of is from "Full of meaning" to "Full of morals" it doesn't seem to (necessarily) be a bad thing... but perhaps the inflection is slanting towards those with less morals who see *it as being pompous.

I see a simple transfer of meaning from one who has a lot of short witty sayings to one who has a lot of short sayings that just aren't quite so witty. Polonius in Hamlet had plenty of short sayings.

Like the pedant who begam a scholar and teacher, to the pedant who is narrow and a bore.