Article III of the Constitution doesn’t really say much about the Supreme Court. It tells us that its members are appointed by the president and confirmed by the Senate; it lays out some jurisdictional parameters; and it sets a “good behavior” standard for removal of justices. That’s it. Everything else is negotiable.
Donald Trump’s legacy is largely a matter of luck; he was able to make three appointments to the Court in his first term as a result of timely retirements and the death of RBG. Obama had fewer appointments than that in two terms in office. By any reasonable standard, that was an unjust result.
Packing the Court is legally possible, but practically inappropriate, as it would invite retaliation and eliminate whatever residual respect the Court continues to enjoy. The best option would be to subject justices to term limits, but that would require a constitutional amendment, which isn’t going to happen. Personally, I think it would be a good idea to enact legislation that guarantees each president one appointment per term. The number of justices would consequently fluctuate with deaths and retirements. So what?