I would say high repetition rate in a canton with high rate of foreign students does not speak for itself in the way it would speak for itself in other cantons. I would not compare Swiss German schools with Swiss Romande, for example. Just my angle at it, since I work in the system, and at a level of exactly that, repeating a class, 10th year if you want. Between high school and secondaire.
Repeating class does not have the same stigma here as it does elsewhere, it can often be an efficient way to immerse foreign kid who is slipping back into the system, often giving chances way more than if the kiddo stayed put in his old class.
The parent who praised Lutry edu environment sounds similar to my la Cote experience. Super high percentage of foreign kids, but very well thrown into the game, even though they might have to repeat the class, in order to make it to Gymnase, for example. To gain points, skills, language aptitude, to make themselves comfortable, because parents often do not know what the system is about, so if kids do not succeed, by the time they are done repeating, they know themselves what they need to do and do not have to rely on parents pushing them.
Implementing HarmoS and the the new voting results will take years in order to fully function. I actually do not mind slower changes in the system, once they work well, with all the important details they need to take, including having enough well prepared teachers. HEP is, by the way, reacting very quickly to the new demands. DFJC, the edu dept in VD, for example, is acting quickly too. You cannot first implement the changes on school level, when you do not have the new group of newly educated teachers ready, or the old ones reeducated. The whole reform takes time on multiple level, and right now, there is a lot going on for teachers, in terms of edu requirements and obligatory licensing.
I would say, go for either canton, but where there is tolerance for multicultures, since the schools will be ready already now, to deal with challenges that multicultural school population means. I am so far happy with the la Cote VD school we are in, the creche level was fab. It looks like the success of the kiddo depends mainly on parental involvement, kid's attitude and teachers interest. Like anywhere else. There is not much point in comparing cantons, though, since the schools vary in the school population and teachers vary in their objectives. Just like kids and their folks. I would not, though, forget, that what parents do with kids at home matters a lot. Homework, etc. it can neutralize a negative impact that comes from official schooling, more so considering that kids have one teacher per one school year, mostly.