Can you post some benchmarks for yours Vega & 5700xt? It need to understand what exactly are horrible with your performance.
Frames all over the place...
"Summary"
"Game Title","Mac","Model","Model Year","Processor","RAM","Graphics","Resolution","Settings","Frame Rate (average)"
"Diablo III","iMac Pro (2017)","iMacPro1,1","2017","3.5 GHz ","32 GB","Radeon RX 5700 XT (0 GB)","","","49.02"
"Computer Details"
"Computer:","iMac Pro (2017)"
"Model:","iMacPro1,1"
"OS Version:","10.15.4"
"Processor:",""
"Processor Speed:","3.5 GHz"
"Processor Core Number:","16"
"RAM:","32 GB"
"GPU:","Radeon RX 5700 XT"
"GPU VRAM:","8 GB"
"Game Title","Diablo III"
"Recording Title",""
"Time Interval",""
"Game Settings"
"Resolution",""
"Graphics Preset",""
"Frame Rate Information (Frames Per Second)"
"Minimum","Maximum","Average",
0.7097,106.3618,49.0206
"Frame Rates"
7.8973
7.8201
8.2559
7.9602
7.9920
7.9920
8.0241
7.9523
8.0321
8.0160
7.9681
7.9920
8.0000
8.0160
7.9681
8.0241
7.9761
7.9761
7.9130
8.1301
7.9681
8.0241
7.8125
8.2220
8.0080
7.9761
7.9681
8.0160
7.8740
8.0890
14.7601
47.0942
37.5865
47.5719
37.4220
34.3474
36.3815
36.5112
36.1809
35.2250
35.0000
35.7498
36.6226
33.9321
32.0641
35.1906
36.6492
3.8212
41.4560
42.3228
43.0862
42.8714
43.1727
42.9448
3.6697
36.0976
36.0721
36.3636
37.4016
38.2696
0.7097
10.1124
7.8973
8.0972
7.8864
15.7534
32.4484
37.0741
36.0721
33.1992
30.0300
32.6409
37.1859
36.7793
39.4867
40.4984
38.4986
41.4560
41.7910
37.6016
37.9242
33.9321
36.2745
35.6789
29.8507
41.0410
42.0420
44.0000
43.1294
39.6040
39.5137
31.8725
35.2823
37.5865
41.6254
39.1174
46.0460
51.5152
44.4664
38.8833
37.6782
46.4427
58.5899
60.1202
60.0000
60.0000
60.0000
59.0000
59.8802
56.9431
54.4554
49.1474
57.4827
58.5859
36.7428
60.0000
60.0000
59.9401
59.0000
55.0000
59.0000
56.0000
59.0551
60.0000
60.0000
56.7951
58.9971
60.0601
60.0000
60.0000
59.9401
57.9858
58.8813
57.5968
59.5960
59.1133
58.5267