You may have been taken in by some black legends about arranged marriages. Catholic arranged marriages always involved agreement of the participants. If you disbelieve the common knowledge that Catholic arranged marriage was once widespread, read the histories of authors like William Thomas Walsh or perhaps take in a few of Shakespeare's plays.
In principle the Church supported free marriage and usually exercised its authority in favor of free marriage choice.
Depending on the time and place, marriage certainly could be forced - or virtually forced. And you don't have to go back to the middle ages. In fact laws were changed more in modern times (for example, in the 18th Century) to give parents more power - and these laws were distinctly anti-clerical in their intent and application.
There are always people who want to use their local influence to be unreasonably domineering. Anyone suggesting that groups like the SSPX should return to arranged marriages should understand the kind of abuses that would be ripe for. Indeed, even without explicitly arranged marriages, abuses are already occurring. The pretty young women are seen as a source of potential revenue.
Prior to the conquest of society by the bankster class, the primary profession of all the noble born was that of knight and soldier. Boys from these families were trained as squires from the earliest ages. The Scottish Catholic Highland clans trained boys in warfare until that culture was wiped out in the mid Eighteenth century. Millitary orders took in boys at a young age. Boys are naturally suited for military training. When I was young, I spent many hours after school playing soldier neighborhood boys using store-bought and make-shift toy weapons.
A military school, or "military discipline" at school, in an SSPX where some priests give sermons against homeschooling - demanding that children go to their schools - is about manipulation and control, and people with a strong desire to control others. It's not about learning to shoot, or training for a future life as a soldier. It's not something for priests to be encouraging.