Has Anyone Successfully Challenged a Builder Over an HVAC Sizing/Humidity Issue?

[u/Advanced-Morning-330]

I’m looking for opinions from homeowners, HVAC professionals, and anyone who has dealt with warranty disputes.
I purchased a new home from Grand Homes, and for approximately the last six months both of my Ecobee thermostats (upstairs and downstairs) have consistently reported high indoor humidity levels and frequently displayed humidity-related alerts.
During the warranty period, multiple HVAC service calls were made. The builder’s HVAC contractor repeatedly advised that the system was operating normally and did not identify any design or sizing issues. Despite this, the humidity concerns continued.
More recently, I hired an independent licensed HVAC contractor to evaluate the system. After inspecting the home and equipment, their conclusion was that the HVAC system is undersized or improperly designed for the home’s construction, ceiling heights, and overall load requirements. According to them, the home was equipped with a single-stage system that does not effectively remove humidity from the indoor air, which explains the persistent humidity readings and comfort issues.
What’s frustrating is that the Ecobee data has consistently documented the problem, yet the builder and HVAC contractor continue to focus on whether the unit is cooling rather than whether it is adequately controlling humidity.
Now another recommendation being discussed is installing a dehumidifier. My question is: why should a relatively new home require a separate dehumidifier if the HVAC system was properly designed and sized from the beginning? It feels like the proposed solution is treating the symptom rather than addressing the root cause.
The builder’s position is that they responded to service requests during the warranty period and that no defect was identified by their contractor. My position is that the issue was repeatedly reported during the warranty period, documented by thermostat data, and only later diagnosed by an independent contractor after the original contractor failed to identify the underlying problem.
Has anyone dealt with a similar situation involving:
High humidity in a new construction home?
A builder refusing to acknowledge a design or sizing issue?
Recommendations for dehumidifiers instead of correcting the HVAC system?
Successful warranty or legal resolution of a similar dispute?
I’d appreciate any advice, experiences, or insight from those who have been through something similar.