I think Shout-Outs are great if handled properly. Like, if you're doing a shout out series, you're doing it wrong. The moment you tell people "you can subscribe and like this video to get a shoutout!" it loses a lot of value. Sure people will do it for the shoutout, but it's not like your subscribers will ever even care.
If you're a channel that does weekly content and you never generally shout someone out, you're going to have a better time getting people to that channel. A sincere shout-out is the best kind of shout-out. It can't be too frequent, and it has to be spontaneous. Take myself for an example. I almost never upload videos. Though when I do they get great reception. So if I were to shout someone out at the end of my videos spontaneously, it will most likely have a greater impact than if I had a video filled with shoutouts and such.
Just my personal opinion.