I’ve always felt that owning the copyrights to your own music was golden as there are many advantages and the payoff can be substantial. As an example: If you have success as a composer and years down the road you want to “cash out” and sell to a larger company, owning a catalog of your copyrights can potentially mean a big pay day. BTW this is done all the time.
Recently I was offered an exclusive deal with a three year term, 50/50 sync fee, 50/50 PRO income and a reversion clause IF the earned income did not exceed $300 in PRO money and/or sync fees. If that threshold was crossed, the library would own the song/cue in perpetuity. In essence they would own the copyright forever.