[CBLT]

HAProxy can be run as a layer 4 load balancer[0]. I think your comment is assuming it's running at http layer?

[0] https://www.haproxy.com/blog/layer-4-load-balancing-nat-mode...

[buzer]

It still requires you to terminate the connection on HAProxy. None of the things I mentioned are affected (you lose source IP without proxy protocol, return traffic must pass thru HAProxy, you can do TLS).