The consilience is due to the decay being proportionate.
If the decay rates had changed significantly at any time in the last 50,000 years, it would be easily seen in the tree ring, lake varve, and ice core records. If the decay accelerated enough to account for a young earth, there would not be any measurable carbon in any ring, varve, or core which pre-dates such an event, since the accelerated decay would get rid of short-lived isotopes extremely rapidly.
Instead, what we observe is carbon concentration in the annual layers consistent with a constant decay rate with variable atmospheric carbon-14 concentration.
So, you would need to come up with a mechanism by which long-live isotopes are affected by a LOT, but short-lived ones, not so much, and result in consilient data.