All of those things serve useful, but slightly different, roles. Emails with good highlight video are helpful in getting coaches interested enough to watch you in a showcase and to look out for you in an ID camp, with the latter two things necessary to get most coaches' interest up to a higher level than the highlight video alone. Coaches get thousands of emails, though, so it's easier to get them read if you have the more prestigious league letters in the subject line and/or if you have a club coach (or a private trainer etc) who has already spoken to the college coach and recommended they look out for you. Moreover, coaches have limited scouting budgets, so it's once again easier to get them to watch you if you play in the showcases (again, often hosted by the prestigious letter leagues) that the coaches attend and/or if you go to the ID Camps where they will be. It's even better if the ID camp is at the school of the coach who is interested in you since you know the whole coaching staff will be there (increasing the chance one or more will be excited by you) and it demonstrates your serious interest in the school. Social media highlights theoretically can create buzz around a player, but if you're trying to attract random coaches that way, be prepared for coaches who are at lesser known schools where they have to beat the bushes to find players. Those highlights are more effective if they are linked to personalized emails sent to coaches.
You can get recruited without some of these steps. For example, you can be on a high-level team in a high-level game and a coach can just notice your player. For that to happen, though, someone on the team probably produced and distributed a high-level brochure with each player's photo, number, position, GPA and other stats and/or someone else invited the coach to attend and they happened to notice your kid while they were there. You can also stand out at an ID camp without sending anything in advance to the coaches. If you want to be the driver of your recruiting process, though, and not just a passive observer, it's better to be the one to get the coaches you want to attend and be on the team that is at the places where the coaches come for the highest concentration of recruit-level players.
There is an element of randomness and luck to the process, but that happens at the level of whether you are on the field when the coach comes to watch you, whether the ball comes your way and/or you have an opportunity to show off for them, whether you are mistake-free when they are watching you (or at least react the way they want you to when mistakes occur), whether they happen to be looking for a player in your grad year at your position, what happens to higher-level players they coach would consider reaches in their recruitment (e.g., the trickle-down effect).
