Since you bring up trends, Xbox is due for a rebound.
PS2 150M, Xbox OG 30M
PS3 and Xbox 360 around 85M each
PS4 115M, Xbox 45-50M
PS5 ?, Xbox Series S/X ?
Aligning launches PS4 is performing slightly better than PS2. But PS4 still is $300, Sony said will continue supporting PS4 for years, PS5 will have full BC so many 3rd party / indie games will continue to be releasing on PS4 too, then there's PS Plus and PS Now on PS4 in addition to Netflix and so on to provide extra content these years to PS4 users...
I think it's pretty likely that PS4 will end selling 150M or close, or even slightly outsell PS2 and become the best selling home console ever and end close to 160M.
Looking at production numbers, preorder selling out in minutes everywhere, exclusive and multi line-up for the first year and how PS5 performed in social media with gaming history records, PS5 seems to be on track to outsell PS4 at least in first weekend, first month, first FY (~4 months) and first year sales. So who knows if it may end outselling total life cycle PS4 numbers. MS is more focused on selling subscriptions than consoles so I think they will offer less competition in consoles than with XB1. Let's also assume console market continues growing as it growed every year since some decades ago.
Remember that PS5 may have the first year 1 AAA exclusive lineup we ever saw with Miles Morales, Demon's Souls, Sackboy, Godfall, Ratchet & Clank, Returnal, Horizon 2, God of War 2 or maybe even Gran Turismo 7 (not counting here timed exclusives from Zenimax or popular indies and who knows if even FFXVI), while Xbox only has Halo Infinite for the first year.
There's also going to be up to 150M PS4 users who are more likely to want keeing their library when going next gen, so BC may favor them to go PS5 to keep their library of games, specially the PS+ library they may have grow over years, and would lose if stop paying the subscription.
Let's say that being optimistic PS5 may sell up to 170M. I personally think 200M is too much.
With all the cloud streaming services, mobile, Xbox trying again, Nintendo being so appealing and the rise/wide-adoption of PC gaming, higher cost to entry, I don't even know if it will sell as well as the PS5 in the same amount of time.
Nintendo it's on the peak year of Switch lifecyle, starting next fiscal year will start to go down. Same year that some AAA multi games will start to be next gen only so decent Switch ports will be too difficult.
When mobile market grew a lot didn't negatively affect home console markets, only the portables. During the recent years PC, consoles and mobile markets grew, only that mobile grew faster. All 3 markets are expected to continue growing. So mobile growth won't affect consoles.
Regarding cloud streaming services, PS Now is the market leader and we know they are working on next gen updates. The other services as of now were just promises (xCloud, Luna) or failures (Stadia, Nvidia). I think MS will perform slightly better with Series X than with XBO but in the long term, during its first year will have a decent launch but PS5 will outsell it with a big margin during the first year, because MS will be focusing more on Game Pass than in Xbox.