Casiokid
The chord substitution you mention in harmony speak is known as a V7 to II substitution, and is the most common chord substitution in music. The two chords are very closely related, and substituting a II for V7 will nearly always sound good, depending on the overall chord sequence, arrangement etc. In fact many jazz players will almost never use the V7 chord regardless of what is written, always substituting it for a II chord. The main difference between how these two chords sound is going to be the bass note, in your case Ab versus F. But in your case you are actually playing a slash chord with an Eb bass in both, so in my opinion the difference harmonically between these two chords is a gnats eyelash, and I doubt most people would even notice it.
But you are saying it sounds 'muddy'. Not sure why that would happen because when you play a slash chord, the acpmnt driven by the style stays the same only the bass note changing. So if it really does sound muddy that would be more to do with how the accompaniment was written in that style than the chord substitution. Another couple of possibilities is the way you are fingering it, maybe you are getting a different chord than you think. Or if you have a LH voice playing, the sound of those LH notes may be the cause, especially if you use one of the shortcut fingering methods.
Either way, you are right to be driven by what your ear tells you. Unless you are in a music exam, how it sounds is more important than technically correct.
People do often simplify chords for the arranger, but usually because they have difficulty with fingering the more complex chords, rather than the way it sounds.
Mike