Most developers who update competitive games will tell players exactly what has changed. Nintendo is not the most developer and often does things in their (frustrating) way. With today's new Super Smash Bros. Ultimate patch, Nintendo has actually given us decent patch notes.
For the series, this is an unprecedented step. For Super Smash Bros. for Wii U and 3DS, Nintendo would change the characters – some stronger and some weaker – with no explanation or details. Players are committed to documenting the updates and comparing a pre-release version of the game's characters (damage, delay and start distance rating) against the performance of the update. It was a lengthy process.
Nintendo took some steps to improve things with Ultimate's first patch, at least telling fans which characters were changed. Today's update, with which the new Piranha Plant Fighter is available, but gives accurate information.
Super Smash Bros. Ultimate was released on December 7 for Switch. It is already a great success. Creating decent patch notes can help to make some goodwill with the fans of Smash Bros. who can turn them into longer-term players (which then results in spending money on future downloadable characters)
For example, we can see that King K. Rool has received Nerfs. His down attack now throws enemies into the ground for a shorter time, and his vacuum-sucking attack now lasts less time. Incineroar has since been improved, which includes an increased takeoff distance for some of its moves.
Hopefully, Nintendo will release more patch notes in the future.