No, I don't think they're in trouble.
When I say that, though, I don't mean to say that I don't think Stadia and Apple Arcade don't have a place in the market. I'm feeling pretty certain that Apple Arcade is going to find a sustainable audience and gradually grow over time, assuming Apple hardware sales continue to be solid. I know Apple's steadily declining in annual hardware sales but I can kind of see the reasons why, but I don't think it's trending in a way that's going to lead to their demise based on hardware sales any time soon. I think the mobile market is on a continuing trend of maturity and will grow to break free from its current perception as a low-end gaming experience, and I think services like Apple Arcade are going to accelerate that maturity.
Stadia is unproven in real-world scenario for the most part. The beta from Project Stream and the variety of impressions about the service from GDC give a mixed feeling about how well it'll work when deployed to actual households on a big scale. If it works, I think it's similar to Apple -- it'll be well enough for some folks to cross a threshold and it might find a market, but I feel a lot less confident that it sustains over time. If anything, I can imagine potential flaws not being enough to dissuade initial interest in gaming, but as time goes on, I think the flaws in the end user experience will either encourage migration to dedicated hardware to continue to grow as enthusiasts or they'll just drop gaming entirely and maintain a periphery interest. I really don't know with Stadia.
The current big 3 have got what appear to be pretty steady platforms with healthy consumer adoption rates that I don't see as necessarily threatened by the introduction of Apple Arcade or Stadia. Xbox did lose a lot of market share and has aggressively invested in trying to maintain or earn consumer faith after squandering much of it at the outset of this gen, but I don't perceive them as being at any risk of downfall. Excitement about the future of the current 3 (Sony/Nintendo/Microsoft) doesn't seem to have waned in the face of the reveals of Stadia and Apple Arcade, but I do think people's dismissal of them is a bit misguided by the perspective of already being rooted in existing service structures. Stadia is a bit easier to dismiss outright due to its largely unproven performance and capability in "real world" scenarios, but Apple Arcade feels like a natural extension of mobile gaming to me, and I think mobile gaming rightfully gets maligned for providing comparatively low quality gaming experiences, BUT people tend to continuously overlook the actual engagement numbers and cash flow of the industry with delusions that its non-existent or some purity test about its validity and place in the marketplace. It may not carry a ton of overlap of audience with traditional approaches to gaming services, but it's definitely there and hasn't really gone anywhere but up since it started -- Apple Arcade makes perfect sense and I think it's going to do well as long as Apple hardware sales don't start to just absolutely tank.