Alolan Ninetales GX is a great helper to any Stage 2 deck, agreed, but I feel that it doesn't change the fundamental problem of Stage 2s needing to run more mandatory cards than Basics or Stage 1s.
Compared to a primarily basic only deck like Ray/Zeraora GX and Buzzwole, you have to run 3-5 Stage 2s (I say 3-5 because Gardevoir decks should play top end heavy with 3 Gardevoir GX and 2 non-GX Gardevoir) on top of 4 rare candies, and basically as soon as Alolan Ninetales GX comes out, you're running a compulsory 2/2 line in any Stage 2 deck. Some people will also run 1-2 of the Stage 1 in between, but I've personally slashed those completely to save deck space, especially with Alolan Ninetales GX guaranteeing candy. But at the end of the day we're looking at an average of 12 card slots that are just absolutely fixed for Stage 2 decks, and Rare Candy & Stage 2 Pokemon are turn 1 brick cards that make playing supporters like Lillie even harder, which puts Stage 2s even futher behind in comparison.
Compared to Stage 1 decks like Malamar variants, Zoroark GX, and Blacephalon GX/Naganadel, you're still up 8 cards running 4 Rare Candy and a 2/2 Alolan Ninetales GX line. Stage 2s like Gardevoir GX used to be a lot better because the "hassle" was worth it, but nowadays we have basics that can hit Gardevoir's numbers with lower/easier energy counts and with more consistent set ups, with or without Bridgette/Elm.
But at the end of the day, the problem with Stage 2s isn't really Rare Candy or any of that other stuff - it's that basic GXs have just gotten too strong, in my opinion (Buzzwole GX, Ray GX, Blacephalon GX, Ultra Necrozma GX, to name a few that already have/currently are/will soon be really strong in the format)
As someone who used to main Gardevoir GX, I don't think Stage 2s are "dead" per sei, but I don't think this is the right time to bring it back. The only Stage 2 I believe in at the moment is the double Solgaleo GX deck (yes I have playtested it against other "good" decks), but even then that still depends on what decks look like by the time we even get those cards.
At the same time, I also do believe that certain decks operate better for certain people. Decks play pretty differently than one another, and people tend to also have different playstyle preferences as well, so playing the "best deck in format" isn't always the right choice anyway. I'm just trying to share my opinion on potential deck options based on my perspective & playtesting results, so hopefully it doesn't seem like I'm judging anyone for whatever deck they want to play.