I just sold my GTX 1070 for a RX 6650XT and it runs much worse than the GTX 1070. I was fully aware of the bottleneck issues as I have a Ryzen 7 1700X but that doesn't mean it would make it run worse. So far, the thing barely runs, and I have tried basically everything but for some reason the GPU utilization won't go past 60 in almost every game and in Borderlands 2 it won't go past 30. I tested the system on Userbenchmark and I scored 99.5% so there's no reason it isn't letting my GPU hit 100%. My CPU won't go past around 40 either. I didn't have any issues like this with my 1070.
My immediate thought is you are running an older B350/B450 or X370/X470 MB. These will be PCIE3.0 x16.
The 6650XT is a PCIE4.0 x8. This means that it is backward compatible with your MB but will only run at x8 speed.
Whilst PCIE4 spec is 2x PCIE3.0 spec (bandwidth throughput so a PCIE4.0 x8 is equal to PCIE3.0 x16), in this case, it is limited to PCIE3.0 but is only using x8 so half the potential PCIE throughput of your GTX 1070.
Looking on Techpowerup, the GTX1070 has a 256bit bus and over PCIE3.0 x16 delivers 256.3GB/s.
Likewise on Techpowerup, the RX6650XT has a 128bit bus and over PCIE4.0x8 delivers 280.3GB/s.
HOWEVER, this means on a PCIE3.0 interface, it only able to use x8 and therefore your memory bandwidth is limited to 140GB/s (280.2/2).
The potential solutions in order of ease and cost are:
1. Make certain that your motherboard (you haven't mentioned which one) is running the latest BIOS and drivers such that a Ryzen 5000 series processor is available and assuming that it does not cut support for your 1700X. Go to your manufacturer website to confirm.
2. Return your GPU (if still possible) and swop it for a minimum 6700 (non XT) which supports a PCIE4.0 x16. This will ensure that you are at least able to use the full PCIE3.0 x16 on the MB. Additonally, these GPU's are likely cheaper than your 6650XT as they are certainly readily available at £315-£330.
3. Or keep the GPU and buy at a minimum a B550 chipset MB.
Hope that helps
Same with RX 6600, it's bad drivers I think. GPU usage variable from game to game, Cyber Punk runs well and GPU usage are 99-100%, RDR2 same. But some older titles runs horible - BFV5 almost unplayable because of stutters, GPU usage jumping, old GTX 1060 provide ideal experience on same settings with slightly lower FPS. Tests show 1-5% difference from PCIex 4 on PCEex 3 version. I tried to help friend with that card, nothing helped (I have thread here on forum), he replaced it with 3050 and all fine now.
For example that stutters almost year now, this random video with R9 and PCI ex4 and stutters.
P.S they can't fix Skyrim (SE or "classic" version) for 7 years for now, GPU usage 20-40%.