The splash parameter is for plymouth. Did you rebuild your initramfs after changing from plymouth-git to plymouth? I am asking because I have plymouth installed and updated my system yesterday and haven't faced this issue at all.
- List all available themes in plymouth
plymouth-set-default-theme -l
which should give something like this
bgrt
details
dr460nized
fade-in
glow
script
solar
spinfinity
spinner
text
tribar
- The default for KDE dr460nized is dr460nized set it as plymouth's theme:
sudo plymouth-set-default-theme dr460nized
Replace the dr460nized here with whatever theme you want or is available in the list above.
This should set the theme to default dr460nized
- Rebuild your initramfs
sudo dracut-rebuild
restart your system and check if adding splash back to grub kernel parameters works. If it does you can make it permanent again if it doesn't well no harm done you can just reboot normally.
Edit: Thanks for @Jeshu for pointing out the errors in the instructions and that they don't work for people without mkinitcpio. I have changed them and thrice checked them on my system this time sorry for the trouble caused. 