The biggest reason your cheap P90 equipped guitar sounds poor is due to the use of ceramic magnets in the pickups. This isn't to say ceramic magnets can't be good in some pickups - they certainly are. But your cheap P90s are made to imitate vintage pickups, making them very much incompatible with ceramic magnets. Even in middle of the road guitars you can find such pickups sometimes. Such pickups are not made to sound good. They're made to make noise and save money. No P90 was made this way in the 50s when Gibson designed the first P90s. When they were first designed, they were designed to sound good, with alnico magnets.
These pickups use dual alnico 2 magnets for singing treble, fat mids and thick bass. These sit nicely between the ceramic rubbish that you can find stock in many low end guitars and boutique offerings (such as our exclusive Alegree pickups). These use high end components, but are machine wound to a rough spec. You'll get yourself 70% of the way to a boutique offering for a fraction of the price.
The specs (neck/bridge):
Resistance: 7.6k/9k
Magnets: 2 x alnico 2
String spacing: 50
Brass dogear baseplate
Single conductor output wire with shield
Wax potted for no microphonics
Supplied with mounting screws