@VinesnBines the link is a good look at submerged cap.
* As a food plant person we are always looking for methods which cut the cost of goods. From a practical point the first benefit of a hold down frame is reduced labor. A next advantage is that as one scales up volumes it works, hand punching a large tank doesn’t work to remove dry spots. Keeping the cap constantly below liquid level will reduce the level mold and bacteria contamination. The pumping technique did not exist before 1910 and became common in the 1930s with electricity,, pumping really is a modern technique which allowed increasing tank size. Last note, ,, Anyone who has dealt with OSHA (had a laborer get suffocate in a tank) will appreciate that on large tanks punching by hand isn’t safe.
* the main negative to a hold down frame that I see is mixing would get rid of high flavor spots, with small tanks any technique as mixing with your hand/ stainless punch down tool will create more efficient extraction of solids off of the skins. Nylon bags with weights will also decrease the extraction efficiency. Pumping leads to channels where the wine flows which are well extracted and other areas with lower extraction.