No, they played the original games. There's to many consistent lore tidbits thrown through the entire game, heck, FO3 includes references to the Midwest Brotherhood of Steel from Fallout Tactics if you go looking on the Brotherhood's computers in the Pentagon.
It's that I suspect they felt Jet was to "iconic" to leave out, plus it had a specific mechanical niche that no other drug from FO1/2 covered (boosting AP points/movement speed) and thus from a mechanical perspective if they wanted to have a wide variety of drugs for people to use they needed that niche filled. You note you like the addition of MedX, that it works for the lore, etc., but it also filled a specific mechanical niche that no other drugs did (boosted damage resistance).
So they were faced with arguably three bad options. 1. They include Jet due to it's unique mechanical niche and just retcon the lore around the drug; 2. They make up a new drug that has the same mechanical effect and have to come up with a lore justification for it*; or 3. they simply do not have a drug in that mechanical niche and thus end up being mechanically retrograde from the prior two games.
They chose option 1 because it, in many ways, is the simplest and maintains item consistency between games while not sacrificing a mechanical niche.
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* On why they didn't have to do this with MedX is simply because MedX is pretty much known by everyone to be the Australia safe rebrand of Morphine, and given the real life ubiquity of Morphine and how it's an OLD drug, everyone just rolled with it since it made perfect sense.