True, that was a bad example since jackass has come to have a second meaning because the usage is so common. However, that second meaning only arose because of the original practice of using the word “is” for metaphorical as well as literal comparisons.
Let’s look at the Greek
Estin- is 3rd person singular active indicative
Mat 3:17 and behold, a voice out of the heavens, saying, "This is My beloved Son, in whom I am well-pleased."
Mat 3:17 kai idou fwnh ek twn ouranwn legousa outov estin o uiov mou o agaphtov en w eudokhsa
So, is Jesus the Son of God, or does he represent the son of God?
Mat 17:5 While he was still speaking, behold, a bright cloud overshadowed them; and behold, a voice out of the cloud, saying, "This is My beloved Son, with whom I am well-pleased; listen to Him!"
Mat 17:5 eti autou lalountov idou nefelh fwteinh epeskiasen autouv kai idou fwnh ek thv nefelhv legousa outov estin o uiov mou o agaphtov en w eudokhsa tsbautou akouete aautou
Again, is Jesus the Son of God, or does he represent the son of God?
Mat 26:26 And while they were eating, Jesus took some bread, and after a blessing, He broke it and gave it to the disciples, and said, "Take, eat; this is My body."
Mat 26:26 esqiontwn de autwn labwn o ihsouv ton arton kai euxaristhsav euloghsav eklasen kai douv edidou toiv maqhtaiv tsbkai eipen labete fagete touto estin to swma mou
This is the same estin.
Mat 26:28 for this is My blood of the covenant, which is poured out for many for forgiveness of sins.
Mat 26:28 touto gar estin to aima mou to thv kainhv diaqhkhv to peri pollwn ekxunnomenon ekxunomenon eiv afesin amartiwn
This is the same estin.
Mar 14:22 And while they were eating, He took some bread, and after a blessing He broke it; and gave it to them, and said, "Take; this is My body."
Mar 14:22 kai esqiontwn autwn labwn o ihsouv arton euloghsav eklasen kai edwken autoiv kai eipen labete fagete touto estin to swma mou
This is the same estin.
Mar 14:24 And He said to them, "This is My blood of the covenant, which is poured out for many.
Mar 14:24 kai eipen autoiv touto estin to aima mou tsbto thv kainhv diaqhkhv to ekxunnomenon uper peri pollwn ekxunomenon
This is the same estin.
So by what scientific logic do you change the estin here to mean ‘represents’? Is means is.