Well, personally, I would say the point where the centrifugal powers took over in Germany was during and after the reign of Frederick II. (the "Heretic King", son of Barbarossa). Frederick spent most his life in Sicily, which he also ruled, and concentrated his efforts there. With the Confoederatio cum principibus ecclesiasticis and the Statutum in favorem principum he ceded nearly all royal rights to the bishops and princes, and the Interregnum following his death ensured that the princes also took and held those rights.
Still, of course, the HRE was a power, but from thereon it went downhill. IMO, at least. But you asked for the point where it was ridiculed...
Then there was the Westphalian Peace, of course. Institutionally, already that Peace left the Empire to be "living corpse". However, only institutionally, as said, not yet in the heads of the people. The imperial vision was still there, which can be seen in the agressions of Louis XIV. in the late 17th century. Nearly the whole Empire rallied against him, even though they werent directly concerned.
The HREGN was in the end seen as ridicolous abnominations due to two processes of the 18th century:
For one, the princes realised more and more just what power they had. Whereas before there still was imperial solidarity, now more an dmore own intersts and realpolitik came to the forefront. Examples for that are of course Frederick II of Prussia and Max Emanuel of Bavaria, who allied with the French against the Emperor in the War of Spanish Sucession. However, even then he still was declared udner Reichsacht (the imperial ban) by the Reichstag.
The other process was the enlightment, and to modern enlightment thoughts the HREGN really was an archaic abnomination. Its no happenstance that it was Voltaire, the forethinker of enlightment, who said the famous quote about the HREGN, neither Holy, nor Roman, nor an Empire.
So, if you want a TL with a more centralised HRE, you should best start with Frederick II, or maybe even his father Barbarossa. However, even late rthinsg can be salvaged, up to the 30 Years War. Afterwards, everythings too late, but people only realised that in the 18th century.