Ask people who live in Forest Hills and they'll tell you it's been a standalone neighborhood for a while now. Neighborhoods tend to merge or split depending on the demographics. Egleston Sq is listed as part of JP, but try telling that to an old-timer and you'll be swiftly told that that is Roxbury. Lately Google Maps shows Egleston Sq as not only firmly within JP boundaries, it's also migrated south from the Washington/Columbus intersection to encompass the whole recently-gentrifying Washington St corridor.
I think the whole fixation on names is bullshit, anyway... only in this day and age are people so hung up on boundaries of things as inconsequential as neighborhoods... half a century ago, yes, there were neighborhoods that were defined mainly by the people who lived in them, but it wasn't a situation where the entire city limits were carved up into regions, each of which was equivalent to the other.
There are some areas that are "just the neighborhood" — ie, Centre St in JP is just JP, — but others aren't really equivalents to neighborhoods. Kenmore Square is like that: you could argue that it's technically part of Back Bay, or "The Fenway" (or Fenway/Kenmore or whatever the BRA calls it now), but I think most people who live in Boston and don't think as much as we do about this stuff would consider Kenmore to be Kenmore. That doesn't
really make it its own neighborhood, at least as an equivalent of Back Bay or Jamaica Plain. But I would also scoff a little if someone said they lived in Back Bay but actually lived on Deerfield Street.
In our overly pedantic and fixated time, where we truly behave as if, if only we could just define and name everything, our problems would be over, we leave no wiggle room for the way a city — or a region — actually functions organically. Boston is more like medieval Germany, with numerous overlapping, sometimes ill-defined, constantly changing spread of principalities, electorates, bishoprics, kingdoms, duchies, free cities, etc, none of which were equivalent to the other. Yes, the city needs neighborhood associations for every square inch and so you can find your map telling you where JP ends and Roxbury begins, but that doesn't tell the whole story. Some squares are too big to really call them "part of" some other neighborhood. Kenmore, Forest Hills, Cleveland Circle, are examples of places that have their own identity, in 2019. And some areas don't really fit into any area at all — the area of all the -bourne streets (between Walk Hill, Hyde Park Ave, and Morton) may technically be JP, but nobody thinks of that area when they hear "Jamaica Plain". It would make sense to call that area "Forest Hills" although I'm sure that 'hood would vociferously oppose such a redesignation, given the cachet of JP these days. Ha, that gets into another thing nobody talks about, which is how race and money influence the wars between defining neighborhood boundaries, but that's another rant.
Anyway, we have to have our territories and names these days so as long as we need to play the game, I agree with you Bronson, it's time for FH to be its own neighborhood. I wouldn't exclude Forest Hills Cemetery, though... rather essential, I'd say.