Need port forward help please

Yes...not sure how successful it would be; but I recall that there's some default rules that rate limit:

https://openwrt.org/docs/guide-user/firewall/firewall_configuration

Name Type Required Default Description
limit string no (none) Maximum average matching rate; specified as a number, with an optional /second, /minute, /hour or /day suffix. Examples: 3/second, 3/sec or 3/s.
limit_burst integer no 5 Maximum initial number of packets to match, allowing a short-term average above limit.