Bourbon can be made at 10000 different combinations in % of grains, thus the complex array of difference in flavors (and proof) in bourbon/whiskey.
Bourbon regulation is it must be 51% corn. The other 49% can be any combination of rye, wheat, barley, etc… so think of a bourbon.
51 corn, 20 rye, 29 wheat
70 corn, 21, rye, 9 barley
60 corn, 38 wheat, 2 rye..
…. And on and on and on and on and on… % mixes galore.
Then mix in proof from 135 down to 90 and any combination thereof…
Whiskey from just one distillery can be an amazing mix of proof and grains..
Thus your Weller example is so diverse ….
Its trial.. and error
One may love a whiskey from a producer but dislike their next offering or style…