Yes, you are right. I think it comes down to how we use the term generally. I think a lot of it is just sloppy language. In fact, I also think a lot of people leave out marriage as a “vocation” when they talk about vocations, but it certainly is! I’ve given a couple talks on vocational discernment and I always make sure I mention married life since so many people just associate “vocation” with priesthood and religious life. It’s especially important because the vast majority of people are called to married life than the others. I think another big part of it is ignorance; I don’t think we’ve done a great job of discussing vocations with youth, or even adults looking for more in their faith life.
You’re right though, it’s certainly more complicated. Like you mentioned, there are married priests. There are also consecrated hermits and virgins, and even those who decide their vocation is to virginity or hermetical life but are not consecrated as such. Religious life is probably the best known vocation outside of Holy Orders and Married life, so it’s mentioned more. And I also think a lot of people use it as a general term for all consecrated life, even though it’s not entirely accurate.
The permanent diaconate is also a vocation, absolutely! It’s usually a vocation within a vocation. There are deacons who are married, single, and religious brothers.
Another example of a vocation within a vocation is that a male religious has to choose between being a lay brother or an ordained brother if their community has both. Being a priest, secular or religious, you may then want to discern your vocation within a vocation even further. Not all priests are called to be parish priests, some are missionaries, some are military chaplains, some (usually religious) specialize in retreats or spiritual direction.
Membership with a third order is not joining a club, but making a commitment to living a certain charism in the world. It is also definitely a vocation, and requires careful discernment. There are married men and women who are members of third orders, but there are also secular deacons, priests, and bishops (including a couple Popes) who are or were part of third orders. So it is also a vocation within a vocation. The approach might also be reversed, for example, I know one person who discerned his call to a third order right out of high school, now, years later, he’s discerning if he wants to live that vocation out as a married man or as a priest.
Secular third orders are not consecrated life. Secular Institutes are, as you mentioned.
In the end, there are as many vocations as there are people on this planet. It’s really just trying to follow God’s call in your life the best you know how.
