New tubes...far more power??

Aside from the possibility that the older tubes were substantially worn out, such that the difference in gain was very significant, it is hard to account for why the new tubes have more gain (not necessarily more power), yet sound so much less desirable.  Is it possible that the tubes are not the same in design or build?  The manufacturer could have changed up something between the two batches of tubes.

In some of the amps I've heard that use the KT150, the sound is a touch too brittle and hard sounding for my taste.  Perhaps, as the tubes age a bit, they soften in sound and you might be someone who prefers that softer sound.    

If old power tubes are worn out, new tubes will sound significantly louder. 

My brother was visiting over holidays and noticed high and bass were missing in my system.   Probably I was used to ... so replaced 16 KT150s and SQ was restored.
Also it takes ~24 hours for KT150 to settle / re-break in.  My tube vendor burns tubes ~200 before testing but doesn't good until ~24 hours of use.