I watched Will (Benson) play CF because that's mainly who played CF when both were options. Brennan on the other hand got more time in the corner spots.
He's likely on the lower end of "MLB caliber" for CF. If you're to put him in the lineup to play CF, you are going to be doing it because you want his bat in there, not his glove.
He's got some skills, and a surprisingly strong arm (OGonz has an even stronger arm but can't field). Not extremely fast and that does matter for tracking down balls. I think he can be extremely good at RF whereas he will always be more "meh" in CF but defense isn't everything. An OF of Kwan, Straw, and Brennan could be one of the best defensive OFs ever because yeah we're talking about 3 talented OFs who all could play CF if they had to.