Well cutting scissors with paper takes a lot less time and energy than holding the paper up and burning it, so not sure something that splits mountain can be compared with destroying a mountain.
The atom destruction is impressive though and may be a power increase cause we don't know if Nasu intended for atomic destruction in f/sn(I'm doubtful he ever thought about it). I'm not really sure there is anything to actually say that Urobachi intended to increase Excalibur's powerlevel, seems like it stayed the same to me.
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We don't know if the mountain in fate was atomized though, it was completely and utterly destroyed though, so it could have been atomized as well. I honestly don't think Excalibur's power level changed at all/ there is not sufficient evidence unlike say servant speeds which does appear to have had an increase.