In theory I have never really understood why hardware should be better in then software, I mean if it is only mathematical algorithms, why would not software sound as good ? . . . .The only bad thing is that it consume a lot of cpu..but sounds very good.
In a way you answered your own question. Reverb is very complex and requires a lot of processing power to do correctly. Software versions on your computer have to compete with the OS, your recording software, other plug-ins, other instruments, etc. In a word most plug-in versions are dumbed down so they are usable in a DAW enviroment with other plug-ins.
Also I Lexicon has released a software version of their "legendary algorithms" called "Pantheon LE" How does this really compare with the hardware versions ?
I have not used it myself but the "LE" in the name is telling. That usually stands for "Lite Edition," meaning not as complex. The PCM70 is the classic Lexicon verb but just about all of those boxes are 20 years old now and I understand some parts like the display are getting hard to find so make sure you get one with a good display.