Shadal on the question of 430 years or 210 years in Egypt

Shadal answers the question in two very interesting ways, on Exodus 6:20:

"We are forced to say that Scripture left out some of the generations between Kehat and Amram, for in [Numbers 3:28] the count for Kehat of all the males from a month and up was 8,600, and he only had four sons as his family, so each of those four sons would [have had to] have 2,150 sons. And behold Amram only had Aaron, Moses, and Miriam. Moses only had two sons, and Aaron four, so how is is possible for Amram, Yitzhar, Chevron, and Uziel to have 2,150 souls [each] in the second year after leaving the land of Egypt? Therefore, one must conclude as I.B. Koppe in his essay, "Israelitas non 215, sed 430 annos in Eagypt commoratos esse," Gottinga 1777, where he said (and Rossenmueller agreed with him) that Levi, Kehat, and Amram were not in sequential generations, but rather other generations were between them. And according to this, one can answer as its plain meaning the number of 430 years that Israel was in Egypt [Exodus 12:40]. And according to this, the powerful procreation of the Israelites in Egypt can be understood, which the Torah did not speak of as an actual miracle.

And the scholar Jost (Volume 1 page 2) said that the names mentioned here are family names, so it is saying that so long as the father was still alive, for the most part the children stayed bonded together as one family (even though sometimes sons would divide their fathers household, as was the case for Isaac and Ishmael in the lifetime of Abraham, and Jacob and Esau in the lifetime of Isaac), and with the death of the father the family would split, and sometimes even after the death of the father they would not split off until some time. So the plain meaning of this section according to his opinion is that the family of Levi remained one family unit, and was called "Levi" for the span of 137 years after the death of Jacob, and then, after Levi died, the family split into three, the names of which being Gershom, Kehat, and Merari. So, the family of Kehat stayed as one unit for 133 years, and afterward it was split into four families. And at the time of the exodus from Egypt, 137 years had already passed, and the Amram family was one family, of which came Moses and Aaron. So if you add together the three numbers of 137, 133, and 137, and add 17 years on that for how long the Israelites were in Egypt before Jacobs death, you have 424 years, meaning close to 430 years. Therefore (he says) whenever it says "the son of Yitzhar", "the son of Kehat", etc, it means "the descendant of Yitzhar", "the descendant of Kehat".