This is literally a GOOD THING. They made it so their phones would reduce their boost clocks slightly if the battery is degraded to the point where the battery can no longer support those clocks in order to prevent unexpected power offs/faults from the processor trying to pull more energy than the battery can output. The underclock is not noticeable in day to day usage and prevents instability due to a worn out battery AND it automatically reverts to the factory clock speed if the battery is replaced and therefore the underclock is no longer needed!
Would you rather your several year old phone be slightly imperceptibly slower at times or crash randomly because that 50Mhz of boost clock was so critical to you?
This is literally a GOOD THING. They made it so their phones would reduce their boost clocks slightly if the battery is degraded to the point where the battery can no longer support those clocks in order to prevent unexpected power offs/faults from the processor trying to pull more energy than the battery can output. The underclock is not noticeable in day to day usage and prevents instability due to a worn out battery AND it automatically reverts to the factory clock speed if the battery is replaced and therefore the underclock is no longer needed!
Would you rather your several year old phone be slightly imperceptibly slower at times or crash randomly because that 50Mhz of boost clock was so critical to you?