This gets very nuanced but the Plexi as we know it is really a very specific subset of the Marshall Superlead from the ~1968 period. Those tend to have no bright cap, or a less aggressive one, and smaller filtering caps that make the amp feel softer/spongier - a bit more JTM45ish. Think Hendrix.
Around 1969-1970 Marshall started transitioning to more aggressive bright caps and stiffer filtering which produces a brighter, more aggressive, rocky version of that sound. That trend continued through the late 70s.
The Agoura Plexi does a good job with the 60s Marshall sound. I shouldn’t bash it as much as I do, as I think it’s fairly accurate for that sound, it’s just not the version of the Superlead some of us prefer.
Fractal solves this by exposing deep parameters for bright cap and filter cap values.
Stadium is still young so I’m really hoping for a late 70s Superlead one day, or a path to adjust some of those parameters. If you’re looking for the 70s Superlead sound the Agoura Plexi just flat out can’t do it.