Inspiron 14 7440, CPU permanently locked at ~400 MHz (x4 ratio) under full load

Troubleshooting Steps Already Performed (All Failed to Resolve):

1. Switched Windows power plan to High Performance / Ultimate Performance; set min/max processor state to 100%.
2. Full power drain / RTC reset: Shut down, unplug AC, disconnect internal battery, hold power button 60 s, reconnect, boot.
3. BIOS actions: Loaded Optimized Defaults; checked for Turbo Boost / SpeedStep / C-States (no relevant toggles to disable aggressive limits).
4. ThrottleStop (latest version, run as admin):
   • BD PROCHOT checkbox greyed out / locked (cannot disable).
   • Deleted ThrottleStop.ini + reboot → still locked.
   • Disabled Turbo → locks to base clocks (~1.3 GHz P-cores possible, but not tested as primary fix needed).
   • Unchecked SpeedStep / C1E (no change or unlock).
   • TPL window: MMIO Lock attempted; PL1/PL2 not editable.
5. Confirmed using original Dell charger; tested on AC power only.
6. Low system temps rule out genuine thermal throttling (package stays ~55 °C max).
7. No dust/buildup; vents/fan appear clean; no recent hardware changes.

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What happens with a more conservative power setting?  There's no way a system this thin and light can sustain maximum performance settings before it throttles.