It is most definitely possible to compare characters from two different stories. It is what we call a crossover. I'm sure you've heard of it.
Looking at game abilities, comparing SotN Richter and LoS1 Gabriel (since LoS2 isn't out and I didn't play Framerate of Fate for obvious reasons) it seems at face value Richter does hold an advantage.
Richter's moves are speedier and more invulnerable. Higher damage too. However this could be argued due to his gameplay mode. Though as a boss in PoR it was kind of similar. He was even more agile though.
Gabriel shows more defense, and is more 'heavy weight'. Not pushed around as easily. Though Richter has 'bigger' 'super moves'. Gabriel is a tank, with much higher defense and seemingly higher raw power.
Further on Gabriel's side, if we want to get into The Forgotten One's (TFO) abilities, TFO seemed to have released the majority of his power to open the portal. He called it back when Gabriel was winning. Gabriel happened to get it instead somehow and then one shot TFO in half like a loaf of bread.
Where as Richter and Gabriel may have had similar 'power levels', once you factor in the power gained by TFO's battle, it mathematically doesn't seem as though Richter could stand a chance.
From what I know of Mirror of Fate
Simon was unable to defeat Dracula on his own, and Alucard had to help with all his vampire powers to stand a chance.
So this seems as though it adds up.
My verdict:
Pre TFO fight? They're pretty even, just with strengths in different areas.
Post TFO fight? No chance for Richter.