Ok, so I have some ideas but I'll divide them between non-cursed and cursed for your viewing safety:
Non-cursed: Look some solo arrangements on popular compositions. One I'll link is David Pasqualini performing his arrangement of Hedwig's theme. I don't know about powerful, but it is virtuoso. I would somewhat consider it classical, but not in the same breath as someone like beethoven/mozart. Others would be Max Loh's arrangement of the Star Wars Main Theme. A lot more classical than the former, but still not truly classical. Again, I'll link his work below.
Cursed: I'd suggest looking at some movie score soundtracks published by various synthesia tutorials, maybe some marked impossible? I know people transcribe a lot of Rousseau's works (note I never condone piracy unless the individual sheet music download cost is above 5$) so if you search for for his pop song remixes you might find some stuff. Channels like Marioverehrer are also targets of piracy so theres that too. Beyond that, look at some pop song covers and see if there are advanced arrangements for those. I don't think you'll find anything worthwhile, but once in a while stuff like that rush e video comes out. There's probably a dozen youtube channels pumping content like that now.
Links:
Hedwig's theme performance:
Apparently he improved it, check the description for the link to the new one.
Max Loh's Sheet music:
https://maxloh.com/sheetmusic/Rousseau's Channel:
Marioverehrer's Channel: