The best thing I ever did to an Epiphone Thunderbird was move the strap button from the upper, well, it isn't really a horn, to the heel of the neck. That's where it is on my Gibson, and it appears to have always been there. I had to move it on a couple Epis. Once the strap button is there, it will balance much more easily.
And, I'm not kidding about being chosen by a Thunderbird. Once you have been chosen, that's pretty much it. You have become a Thunderbird player. It doesn't happen to everyone who picks up a Thunderbird. I didn't set out to become a 'Bird person, but I had one and liked it. Then I let it go. A couple bass guitars later, I had to admit the mistake and find another Thunderbird. That one started life as a Pro IV similar to yours, but it's now fretless and passive. That led to a Gibson Thunderbird, more recently. The Gibson replaced a Rickenbacker that I don't miss very much at all.