I generally agree with Moose that - at least historically - the key to program-building has been to develop a pipeline of rotation players who you can develop over 2, 3, 4 years so that there is always someone in the program who can step up when the upperclassmen leave. In that world, transfers and JUCOs are fine as plug-ins when needed, and can make a real difference in a team that already has most of its players in-house.
And I've been somewhat vocal on this board that people should put less value on a recruit's star rankings because a good staff with an eye for talent and the ability to develop that talent can get you pretty far regardless of the "stars" - they can come along later.
BUT - having said that, I just don't know if we live in that world anymore. The new normal may be a lot more roster turnover than we've been used to (well that college basketball in general has been used to), and it's going to affect the way you build your team. It's going to be harder and harder to hold onto the talent you're trying to develop, and easier and easier to acquire talent that someone else was developing.
In addition, from a SJU standpoint it is really important to keep forward progress going and to take a big step forward if possible. That would immensely boost the chances of the program thriving in what's likely to be a "rich get richer and poor get poorer world." In that landscape, you need to position yourself as one of the rich to attract players.
I don't get bogged down in "most important recruit ever" or whatnot, but WRT Alvarado there's no question that he's a guy who would be a real difference-maker and would put SJU in the conversation for top-3 in the league. And if you have an opportunity to do that, you do it. It's true it would give us 4 or 5 likely departures next year, but if all goes well the 3 freshmen this year will be ready to fill some of that gap, there will be more freshmen behind them - and the transfer portal will still be there and maybe even more fruitful if it involves coming to a good and rising program, which Alvarado would most certainly help us be.