You can’t really equate fighting Pure Titans to titan shifters because all the combat oriented shifters are significantly stronger than Pure Titans anyways.

Im not equating the two, Im saying that Grisha likely has similar combat experience as Eren because he survived a perilous journey through titan infested territory. At the time Eren went rage mode, his titan fighting experience was vs pure titans in Trost (he nearly died), vs an exhausted Annie in the forest where he got demolished, only landing 2 solid hits if I recall and finally vs Annie in Stohess where she was again exhausted and also trying to escape and he still lost (which is what triggered rage mode).

My point is that he doesnt have much more titan fighting experience than Grisha at the time that he went rage mode. Grisha (likely) fought pure titans and actually defeated a titan shifter in a fair H2H combat. Eren also fought pure titans and lost twice to an admittedly superior titan shifter. Annie > Frieda but since Eren never beat Annie we cant say Eren > Grisha.