One of the reasons 5G seems worse is because most implementations are NSA (non-standalone) right now. As others have mentioned, this means you're using the LTE network for control/signaling and 5G just for data traffic. 5G SA improves latency because it ditches the LTE signaling but it's not available everywhere on most operators yet. Verizon and AT&T are just starting to implement it. T-Mobile US has been ahead of the curve in offering 5G SA nationally for a bit now.
However, probably the most important reason 5G performance can appear worse is because NSA works via a technology called ENDC - EUTRAN New Radio Dual Connectivity. This enables your device to receive LTE from one cell site and 5G from another. LTE being there to carry the control/signaling as previously mentioned as well as improve speeds by combining LTE and 5G channels.
When you're receiving 5G from one site and LTE from another. Depending on your device and your network operators settings, more of that traffic will flow over either LTE or 5G. If your 5G channel conditions are poor (say 5G is coming from a far away site but you're also on a closer, LTE-only site), but your device is still preferring to send data mainly over the 5G leg of the connection, you could potentially see worse performance than you would on LTE alone.
However, probably the most important reason 5G performance can appear worse is because NSA works via a technology called ENDC - EUTRAN New Radio Dual Connectivity. This enables your device to receive LTE from one cell site and 5G from another. LTE being there to carry the control/signaling as previously mentioned as well as improve speeds by combining LTE and 5G channels.
When you're receiving 5G from one site and LTE from another. Depending on your device and your network operators settings, more of that traffic will flow over either LTE or 5G. If your 5G channel conditions are poor (say 5G is coming from a far away site but you're also on a closer, LTE-only site), but your device is still preferring to send data mainly over the 5G leg of the connection, you could potentially see worse performance than you would on LTE alone.