Laekens are not as widely selectively bred to be super competitive sport dogs the way some lines of Mals are. So you can probably expect them to be a more moderate dog than
some Mals. Although I use the word moderate lightly, Belgians are generally quirky, complicated dogs in their own ways. Any good Belgian should be drivey, willing, into doing stuff with their person, athletic and intense about their "work".
It really isn't as simple as saying "BYB Mals lack drive". Mals are in a bit of different situation than say, GSDs. In GSDs there are show, working/sport and pet lines (and a lot of variations within them). The "pet lines" are what you are calling "BYB". With pet bred GSDs, their pedigrees show generations of pet dogs being bred. No known kennel names, no known dogs and dogs being bred just for pets. Mals, it's a bit different. There are not really "pet lines" in them the way you see in GSDs. In GSD rescue, the vast majority of dogs are pet bred from pet bred pedigrees. There is not a separate population of Mals which have been bred for the pet market. What there is though, are unethical breeders hoping to cash in on the popularity of Mals as police, military and protection dogs. These breeders tend to have working/sport line Mals but they may or may not be actually doing anything with them. Some of them undoubtedly have dogs who are sport or work wash outs. They sell puppies and adults to whoever wants the dogs and if things don't work out, they won't help the owner. Some sell "trained adults", although that's certainly a buyer beware situation too. Anyway, these are largely the dogs you see in ABMC rescue. Plenty of those dogs do have drive and are definitely characteristic of Mals in temperament - if they weren't, well there ABMC probably wouldn't be so busy rescuing them. They are not "pet bred", they are from working/sport pedigrees. It is a very odd situation and rather different from how it works in most any other breed.
I'm sure there are people out there doing herding with their Laekens but they aren't much like Collies at all
Epilepsy in the Belgian breeds is not an issue of "BYBing" or popularity. Wish it were that simple though!
This is detailed info on the coat genetics of the Belgian breeds.
http://www.belgiansworld.com/belgian-shepherds-info-coat-genetics.htm
Degree of sociability in the Belgians can vary even with individuals within a litter. While the ideal should be dogs who are "aloof" towards strangers, it's rare for an entire litter to all be ideal in any area. When aloof is the ideal, you will get dogs who falling outside of the ideal who are suspicious or weird about strangers. I suspect that being anti-social is a trait that probably goes back as far in their history as you can trace. Modern times generally don't call for dogs who are suspicious of everyone and over time, I do think that has been bred away from in it's most extreme form, even within the working/sport population. However, dogs who are very suspicious, intolerant of stranger interaction and very naturally guardy do exist within all of the Belgian breeds/varieties and in all lines. My friends and I have taken to referring to these dogs as "No Touch Belgians", fondly since we've all known and loved at least a couple such dogs. On the opposite end of the spectrum, I've known and owned some very social Belgians. And I'd say many are somewhere in between. There really is a quite a range and where an individual falls depends on both genetics and experiences.