I was scolded by a boss for using words that to me were perfectly ordinary everyday words. Words like "cognate" or "cognizant", say, but to him they sounded like I was showing off and making people feel bad.
That's a different issue from sandhi. Vocabulary and dialect are another area of active study (often paired with yet another realm: sociolinguistics: the language you speak changes according to your social environment) that is a real rabbit hole.
Sandhi is a real thing. (Source: I had to study this shit to teach pronunciation classes.)
It took me WEEKS to recognize that what I thought I was saying and what noises I was actually making are completely and utterly different. There's often no relationship (like "coodja" for "could you" or "chrain" for "train") between the intended sound and the actual sound ... but since everybody does it you don't notice until its forced into your face. The only time you make distinct sounds as per the "official" description (and even then not as often as you think: I submit "train" once again as evidence) is when you're deliberately speaking slowly and distinctly. Which is almost never (and comes across as condescending in actual interaction).
Weeks, I say again. WEEKS. And this was under constant training that included the playback of what we'd actually said showing us what we were doing. The denial is embedded deeply in our psyche.
If you're a native-level speaker, no you don't. You think you do. Assimilation is a real thing and is a huge part of all native language. NOBODY pronounces the way they think (and often loudly claim) that they do.
Just like the people who claim they don't have a "j" sound in "could you".
