There is a class of interior defensive linemen who make significantly more than any interior offensive linemen. Right now there are three of them-- Aaron Donald, DeForest Buckner, and Chris Jones (20-22.5M in AAV).
This makes sense, as these are players who can take over games single-handedly. All positions on an NFL field are interrelated to and affected by other positions, but some are less dependent than others on what goes on around them. These would be three such players. Donald or Jones can wreck a game even if the edge guys are having a terrible day. You don't really see this with interior offensive linemen, where they single-handedly wreck a defense (though they can still have tremendous individual impact, especially in neutralizing a guy like Donald).
Now that said, once you get beyond that top shelf of elite game-wrecking players, the salaries would tell you that the league sees iDL and iOL as basically comparable in terms of value. The really, really good ones get between 14-18M in AAV. On the defensive side, that's guys like Kenny Clark, Grady Jarrett, Cam Heyward, while on the offensive side, it's guys like Brandon Scherff, Joe Thuney, and Brandon Brooks.
So if you just set aside that special class of iDL player, the two positions are comparable. As Clark is not in that special class (he's very good; he does not impact the passing game like those others), it doesn't hold water to say that he's more valuable than Jenkins by virtue of his position. Allowing that Jenkins continues on his current trajectory, his second contract will be rightfully comparable to Clark's.
And all of this is basically moot because Jenkins is on a rookie contract, which makes his overall value far greater than Clark's even if you believe that iDL has a significantly greater positional value.