I moved your post into a separate thread. Use this thread to ask for help:
https://forums.dolphin-emu.org/Thread-xmen-legends-error
It's better to make your own thread instead of hijacking someone else's. It keeps things more organized since we don't know the details of your situation (Have you updated your drivers? What settings are you using? Have you tried reverting to 5.0 instead of 5.0-12380?).
I get around 45fps too, at least in Legends 1. If I remove the limit it goes above 100 so I don't think it's a problem of processing power. It might just be limited by the game. On the actual Wii the frame rate feels even lower so I can't complain too much.
I am running into issues getting widescreen to work well, though. Using the 16:9 gecko codes that I found on the wiki, most things work fine, but the text in the UI runs together in a lot of places. The powers menu is the worst, with many things overlapping and running outside the menu board. I think it's increasing the font size or something without actually having more room. I can try to get screenshots later. The widescreen hack works better for the UI (stretched but more usable) but has issues with objects getting culled outside of what would be in the 4:3 view
I know the last post is from August, but I thought I'd chime in on this since I just experienced the issue with X-Men Legends 1. Running Dolphin 5.0-14209 on a 9900k with an RTX 3080.
Uncapping the emulation speed does indeed send the speed into the hundreds of FPS, which indicates it's not a hardware problem. I also tried using an external vsync and FPS cap to see if this would alleviate the issue, but in both cases it only seemed to cap the FPS during gameplay. Menus and videos were still at the uncapped speed. Sound also seems to generally run faster.
Obviously it's a different emulator, but I encountered a similar problem when I tried running Folklore on RPCS3. No matter what I did, I kept getting sub-30 fps performance in a game that should easily exceed that on my system. To fix it I had to apply the 60 fps patch created for the game and then cap the frame rate at 30. This somehow made the game work at a perfect 30 fps when before it never went above 27.
I'm going to do some digging to see exactly what can be done to pull off something similar in Dolphin. I'm thinking the game may simply have a weird FPS cap hard-coded into it.