The problem is that currently max texture size you can load is 16,384 in any dimension for Dx12 and Dx11 and you can't do anything about that. The lower version user supports, the smaller maximum size they can use. For example user with Dx10 users won't be able to load an image bigger than 8,192. Users with Dx9 won't be able to load bigger than 4048 and so on. HiDef only says to use DirectX bigger than 9 if possible I believe.
For you there are 2 possible solutions, depends on how many users you want to support. As I understand you only assembled spritesheet horizontally (50x1)?. You should always assemble sprite sheet vertically also, for example in lines of 10 images (10x5). However based on your image size it would still be pretty large. Other way would be to separate images to separate files based on sequence "splashscreen_01.png", "splashscreen_02.png"... Loading this should be very easy in an array.
I personally assemble my own atlases in game based on user max supported texture size from sprite sheets or separate images. But this can take a week to code and assemble nicely.
If you want to support as many users as possible, then the maximum texture size you should target is 2024.
I hope this answers your question.