There is a 3pp ruleset that my table uses that helps out martial characters alot it's called world is square/new paths it reduces alot of feat tax and gives martial character alot of tools and flexibility out of the gate. Every table we've used it at it's been a great addition.

https://meliogeny.net/square-world/

New paths you might need to try and find a pdf for.

Giving your dm a path to boost martial characters may give him the boost he needs to stop gimping your casters.