A force ghost using the force in the living world has the potential to open the floodgates. In all canon, the cosmic force and living force would just simply communicate with each other, now it's reasonable for a force ghost to involve themselves in fights. You can call that nit-picking if you want, but to me I bet they simply gloss over it and force ghosts won't interact that way again. It simply comes down to cosmic force and living force and how they interact with each other. If you prefer it this way fine, but it goes against what was presented to us during the Clone Wars show.
A force bond/connection has already existed though, Rian just expanded on it. It's not different from Luke and Vader and Luke and Leia from the OT. The difference is that in the OT, you could of thought it was because of family connection or being close enough to that individual. Snoke was thought to be this uber powerful dark force user, so I don't think it's too crazy for him to be able to do what he did. There is a piece of it that is a bit weird, but I won't go into that until 9 comes out.
But it shouldn't be too crazy that Yoda was able to do what he did either. You're right that if it ends up being abused as a way to shove dead characters into action sequences it can get pretty absurd, but I'm pretty sure they know that. And it's not like Yoda popped in to intervene in Luke's astral projected "fight" with Kylo. Or the throne room fight. He just set a tree on fire as a symbolic gesture. I doubt it's going to become the MO.
And it's not a matter of what I prefer it's just a matter of fact that as Star Wars continues to make films, it will occasionally show us something with the Force that we haven't seen before. You seemed fine with Kylo holding a blaster shot in stasis and had a rational explanation for why it made sense. Then you have a well reasoned argument for why Rey/Kylo's force link made sense.
What I'm saying is, sure Clone Wars had their explanation of the living force and cosmic force but that was based on an understanding of the Force at a time some 65+ years before the Last Jedi's events. In between that time it's shown that on some level, most Jedi don't even know how to commune with the dead (personally I still find it silly that Lucas felt a need to give some rational explanation to communing with Force ghosts since he portrays it as some acquired talent but then all of a sudden Luke can see Yoda, Ben, and Anakin with no training in how to do so) and Obi Wan needed special training to commune with Qui-Gon, and presumably learn how to commune from the afterlife.
Also in that time Yoda spent a long time in solitude on Dagobah where he could have learned how to expand on his knowledge of the living/cosmic force. And it can be said that a brilliant mind like Yoda's could have, in the afterlife, done more to expand on the scope of his abilities in death than most sentient souls in the force ever attempted.
As long as we're in agreement that the force link isn't that dumb I'd say, while still accepting its place that Yoda using lightning from the dead is still more plausible to me than that, and more plausible than Luke astral projecting himself to death (which I also don't have much of a problem with).
You're right that it could present a problem going forward (though I doubt it actually will) and there's reason for concern. But as for it not making sense as a matter of lore, I don't see the issue.
