Maybe a clarification is necessary.

WHY is shrinking the database weekly so bad?

Firstly, the database is likely to grow again throughout the week. Growing a database file can be an expensive operation, especially without instant file initialisation, so we try to avoid that by not pre-shrinking the database.

It will also cause filesystem fragmentation. Filesystem fragmentation (with mechanical rather than SSD drives) will cause slower I/Os. If you're lucky enough to be working in a pure SSD environment, then you care less about fragmentation as there's no disk head to move.

The only parts of the database that will be fragmented are the most recent extensions, but in an OLTP environment this is likely to be where the reads are happening.

Finally, the shrinking isn't going to have much effect in this case, because the next operation that happens on the maintenance plan is the re-index. That will regrow the database significantly as it re-indexes clustered indexes. This destroys the point of shrinking the database, as well as slows down the index rebuild.