I posted an updated SentinelWinder pic with higher quality (they been posting their pics on Twitter, some with higher quality than their original FurAffinity quality)

The pic from SentinelWinder's Twitter: https://pbs.twimg.com/media/GQqH0tPXMAAuik_?format=jpg&name=4096x4096

Compare to the post from the FurAffinity source: http://static1.e621proxy.ru/data/4f/cf/4fcf865896cd10e6934e7e3fd7a44319.png
https://d.furaffinity.net/art/sentinelwinder/1610963158/1610961874.sentinelwinder_sonearbustyfullbody__text_wip_2___2_.png

However when I posted the pic with higher quality and flagged the older one...the new one with higher quality got deleted instead.
https://e621.net/posts/4894044

This post was deleted or flagged for the following reasons:
[DELETION] Inferior version/duplicate of post #4704585 - DubsTheFox - about 3 hours ago

Help?

(Maybe it's my fault for not fully understanding for not knowing how the replacements work)

Resolution is not the only factor in determining quality. Png is usually preferred over jpg because png uses lossless compression while jpg uses lossy. There are cases where the twitter jpg is accepted over the FA png, but in this situation (jpg resolution < 4x png) that file is kept.