Oak tree health questions

Alright I have a feeling I’m not gonna love the responses I get to this post but here goes…

I have a massive oak tree growing directly behind my house that extends basically over my entire house. It’s massive, and we’ve been told it’s over 100 feet tall and probably over 300 years old. We noticed some die off in the trees crown and contacted a tree service. They realized that when the house (and neighborhood) was built a hundred years ago, the backyard was filled to level the yard which lies on bedrock. This process apparently buried the trunk FEET underground. This stupidity was rather shocking to me but whatever. The tree service dug out the soil around the tree in about a 3 foot ring down to the root flare. They then filled this round pit with cobble sized stones . They said this would help prevent further rot in the tree giving a chance to heal. A few years later now and we’ve had them back to trim (they trim every few years. They said there was some good growth in the crown but also some die off still. I also noticed some giant shelf mushrooms of some sort growing out of the side of the tree for a few years now. I remove them when they grow but idk if that’s doing anything. The tree also has multiple support cables in the canopy that have been installed over the years. It’s a beautiful tree and I’d hate to have it come down, but I’d also hat to have it crush my or my neighbors houses. I guess I’m just wondering what the outlook on this tree is and if I should find a new tree guy. What do we think about the advice I’ve received so far.