In the NBA’s 80 year history, only two teams that were not a top three seed in their conference have ever won a championship. It hasn’t happened in 31 years, and both exceptions were defending champs. 2⁄3 of the time, one seeds win it all. Currently, one seeds have won the chip three years in a row
Looking throughout league history, the outlook looks extraordinarily bleak for lower playoff seeds, and pretty conclusively refutes the idea that the regular season does not matter.
The only exceptions were the 4th seeded 1969 Celtics in Bill Russell’s last year, and the 1995 Rockets with Hakeem, both of which were defending champions.
https://www.landofbasketball.com/championships/champions_by_seed.htm