From your own image, you can see that the PC segment is the smallest, Mobile and Consoles outweigh it.
Also, devs already code for Android and Apple Store and all the apps are there - Office, internet, games, videos, anything you want.
You can do with your smartphone 2 to 3 days normal load, and this with its very small battery capacity.
Show me a x86 notebook that can last 2 days on a battery? That's 48 hours!
Yes, it's smaller, but it's far from being "niche" 24% is a lot of money, that's not what you call a market worth being ignored . Remember how windows phone couldn't get apps even when they tried to make it easier for devs ? Apple got an edge because of the surface pro already having apps like procreate and affinity photo...who are both ignoring android even thought the galaxy tab S6 is a thing.
Light users won't really care, but the people mixing apps like photoshop, after effect with c4d, maya, 3dsmax, are not going to make a switch until everything is smooth...wich is going to take a while seeing how qualcomm focus isn't on high performance yet.
And again you talk about phones lasting 2 days when comparing them to x86 notebook when the arm notebook that are currently on the market can't last 2 days, and do barely better than their current x86 counterpart.
I get that arm got a few advantages that looks neat. But the picture that I see so far show me a futur where Arm and x86-64 are going to co-exist. The former on notebooks for light task, the latter on computers that will be used for heavy work/gaming.
I'm a multimedia infographist, and so far qualcomm hasn't teased anything that could replace my current workstation, and a fair amount of the apps that I'm using haven't talked about an arm version, and don't currently have an android/ios equivalent. You can't say that a new product will kill an older product if he can't fully replace it without hidering a userbase that still matter even if they are not the majority.