I agree that the same sound as "let" or "bet" is more euphonius. I had been surmising someone was suggesting it should be like "beet"!

> no "Swiss patois"

Tell that to my sister, who lives there! There are arguably several forms of patois as all the languages merge and attach themselves to core elements of each other in typical patois style. You haven't seen disdain until faced by a 'High German' speaker sneering at the yokels speaking "this low barbarian speech", or the Italians spluttering at the indignities foisted on 'the beautiful tongue' ~ and as for the French...!

a. F. crétin (in Encycl. 1754), ad. Swiss patois crestin, creitin:—L. ChristiQnum Christian, which in the mod. Romanic langs. (as sometimes dial. in Eng.) means ‘human creature’ as distinguished from the brutes; the sense being here that these beings are really human, though so deformed physically and mentally. (Cf. natural.) So, according to Hatzfeld and Darmesteter, the Cagots are called in Béarn crestiaas.]

One of a class of dwarfed and specially deformed idiots found in certain valleys of the Alps and elsewhere. Also in weakened sense (esp. in form crétin): a fool, one who behaves stupidly. Also attrib. and transf.
1779 W. Coxe in Ann. Reg. ii. 92 note, The species of idiots I have mentioned+who are described by many authors as peculiar to the Vallais, are called Cretins. 1834 Medwin Angler in Wales I. 239 The Cretin is hardly a human being+They have all immense heads and more immense goitres. 1879 Khorz Princ. Med. 4 The offspring of persons with goître are cretins without goître. 1884 W. James Coll. Ess. & Rev. (1920) 270 Bodily commotions+may be experienced in their fulness by Crétins and Philistines in whom the critical judgment is at its lowest ebb. a1930 D. H. Lawrence Pornography (1936) 75 The blood in the body stands still, before such crétin ugliness. 1933 J. Joyce Let. 13 Aug. (1966) III. 282 The crétin of a concierge+has misdirected half my mail. 1961 I. Jefferies It wasn't Me ix. 123, I know I'm a moron and a cretin like you're always calling people.

Hence "cretinage.
1820 H. Matthews Diary of Invalid 314 Cretinage seems also to be peculiar to mountainous regions.


OED2