Examples include: 是、去、在、要、就、但、没有、如果
Not sure how to back up this question, except to mention that I've received feedback from natives that I tend to overdo these words' pronunciations (especially 是）. I've also seen 是 labelled as shi0 instead of shi4 in a few textbooks. Also, when I listen to native speech, I am under the impression that a handful of words in a sentence are naturally (perhaps automatically) glossed over/sped up in order to stress the more important words in a sentence (and, for natives, this I imagine is done for the sake of convenience too).
From these observations, I've surmised that the tones of common words in daily speech are usually glided over more rapidly than other words that are not as common (particularly in situations where it is clear which word is intended e.g. 我是学生 cannot be interpreted as *我时学生 etc).
Is there any credit to this hypothesis? Is it okay to do the same as a learner i.e. to glide over some of the more commonly spoken words in a regular conversation?
words where it is important to distinguish between the neutral tone and the citation tone especially @L Parker's point number 5 on quasi-neutral tones