It would be nice to hear an Italian teacher read this article
In my personal opinion (not at all an expert on languages) an English speaker should work mostly on "gn" and "gl" since in Italian they form a single sound together while English speaking people split the sounds in two parts like "g-n".
It would have been better if Italian just kept using the letter [j] - it was invented by an Italian guy to solve this kind of ambiguity after all.
I saw it still being used on some street signs. Jonio, Jesolo, ...
https://forvo.com/word/piet%C3%A0/
Perchance you're speaking a dialect? Happens to all of us. :)
Not a native speaker and my Italian is terrible, but I've always loved the Italian i vowels. They are so clear and distinct.
Or maybe it's like someone who can feel that the proper plural of "figlio" (figli) would have a long "i" (figlî, in some old books) even if it's not really there anymore.
For instance, piede is /'pjede/, while tuorlo is /'tworlo/.
IPA in Italian dictionaries is very rare, but the only examples I found specify /'pjeta/. Italian pronunciation has never been standardized by anyone, so pronunciation may vary, but unless my knowledge of phonology is completely wrong there's an appoximant in "pietà", like in pieno /'pjeno/ and piano /'pjano/.
To avoid i to switch to /j/ there needs to be a "iato", which splits words onto two separate syllables. For instance, mormorio is /mormo'rio/, not /mormo'rjo/. In this case, the word gets split in syllables as mor-mo-RI-o, and the i doesn't become an approximant. Pietà is pie-TÀ, not pi-e-TÀ, because the ie is in a diphthong, so it's /je/.
... and on double consonants (like BTW a number of Italians, which regional pronounce can be quite opposite, as an example venetians making any double single and romans making most single doubles) ...
The "j" was once used in writing too, called "i consonantica" when it is followed by a vowel, it remained in historical names like Jacopo but became a "normal" i in - say - acciaio (that was once written acciajo).