Quick take
For 7+ bathrooms, 20+ GPM service-flow systems become relevant. SpringWell CF+ is 20 GPM with 1.5-inch connections; RKIN CS13 is 28 GPM service / 41 GPM peak with 1.5-inch connections.
Why standard residential systems may be too small
A 9–12 GPM system can become restrictive when several showers, appliances and large fixtures operate together.
SpringWell CF+
SpringWell lists CF+ for 7+ bathrooms at 20 GPM service flow with 1.5-inch connections.
RKIN CS13
RKIN lists CS13 for 7+ bathrooms at 28 GPM service / 41 GPM peak with 1.5-inch connections.
Large-home installations need system-level design
Meter size, pressure regulator, main-line diameter, softeners, recirculation and other treatment stages should be evaluated together rather than choosing one filter from bathroom count alone.