If it really bothers you, it's easy enough to alias those letters to the commands that you do want, which is probably better for flexibility and whatnot. Adding in single-letter commands would probably be too hard to remember for most people.
h='history | tail -n20'
l='ls -ltrhG'
d='dict -d wn'
s='du -sh * | sort -h'Quick shoutout, you should probably alias to 'du -sh -- *'. Otherwise file names starting with '-' are interpreted as input for your command.
While they arent a single char I do like these a lot:
gs='git status'
gl='git pull'
gcm='git commit -m'
ga='git add -A'
gp='git push'
gst='git status'
ga='git add'
gc='git commit -am'
gl='git log --graph --pretty=format:"%h %Cred%s%Creset %Cgreen(%cr)%Creset" --abbrev-commit'
glh='gl | head -n5'
gp='git push'