There is a particular amount of power any given tube type can deliver. If you push a tube harder to deliver more power, you compromise other aspects of performance, particularly the life of the tube. Tube life can be dramatically longer if a tube is run conservatively but so few companies do so these days because they want to claim a high output.
Every design choice has advantages and shortcomings. Parallel SETs mean doubling output tubes, which means, a high expense when 300b’s are the tube type, and they can be quite hard on the tubes; there is a tendency for one tube in a parallel pair to quickly become weak while the other does the bulk of the work. Pushpull 300b amps will deliver much more power and will typically have a tighter, punchier sound than a SET amp, but the sound is different, and if you seek the SET sound, you have to accept lower output.
While not exactly the same sound as a 300b SET, there are some higher powered tube types, like 845s and 211, that sound quite good. But, decent designs with these types of tubes can be expensive because the higher voltages involved.