You still need both. And you still need to recruit and build relationships with high school kids. Because if a year or two later they're unhappy with their situation at another school, then you'll have already built a relationship with them. And while a couple of coaching staffs have used the portal for massive roster turnover, I think that's best for new staffs. Otherwise, it's primarily for filling the gaps left from players leaving/graduating, and replacing players who aren't developing well enough/properly.
So, YES, you need to be heavily focused on the transfer portal, but you can't just be like "no point getting high school kids". It's not like every one of those kids, or even every one of the BEST kids will leave.