Good, reducing the size of an image will not give you more sharpness,
indeed, it will possibly make it worse and with each conversion step it will become more blurry,
as you have been told, this was not prepared for those resolutions,
and neither You can put images four times larger, simply because the wheel will go very slow or stumbling,
solution to that, because I would download new images at maximum resolution,
and make a single transformation of size and aspect to 16: 9, trying not to exceed 400x175 more or less,
and not using web apps or even photoshop, I recommend the animate program, do the test with one and you will tell me.
All the best