Yes, it is valid that there are no currently proven references to an "Israel" previous to Merneptah.
The Merneptah stele tells us essentially that, somewhere in central Canaan, a people named Israel existed, considered enemies of Egypt in 1210 BC.
The association with the Israelites and the Hyksos was made as early as 250 BC by Manethon of Sebennytos, and Josephus, Flavius in the 1st century AD.
Many scholars feel that the biblical story of Joseph rising to power in Egypt tallies with the political realities of the Hyksos era, and indeed the time-frame of these events seems to fit; between 1750 and 1550 BC.
As for the association of the Hyksos expulsion and the Exodus, there are pros and cons for this argument. The general feel of the Hebrew narrative indicates Ramasside slaves migrating from Egypt to Canaan, whereas the Hyksos expulsion is the destruction of a dynasty and expulsion of a population--which seems to date to Jacob or Joseph era events? Perhaps in the end, the biblical authors composed their saga on early strands of information they had available,--a dynasty fleeing Egypt, and Hebrew slaves escaping harsh bondage in the quarries and mines of the New Kingdom.