Hi,
Regarding the file size increase, the Copernicus Data Space Ecosystem (CDSE) uses the zip format as a way to distribute multiple files (the content of the SAFE) as a single archive but they do not apply any compression, whereas the zip files previously distributed on scihub.copernicus.eu had compression enabled. The switch between scihub.copernicus.eu and the CDSE happened in November 2023, so that would explain the size difference.
The problem has been reported by several users on the CDSE forum, for example: https://helpcenter.dataspace.copernicus.eu/hc/en-gb/community/posts/14515808649757-Changes-in-Sentinel-1-SLC-product-zip-file
In that thread CDSE support says that compression would be enabled by the end of February 2024, but it does not seem to be the case yet. If download bandwidth is the issue you will have to wait until CDSE implements compression unfortunately. If local storage is the problem, then uncompressing and recompressing the zip as suggested by @ghajduch should reduce the size of the file significantly.
As for the IW3 sub-swath, other users have been facing the same issue and the workaround for now is to uncompress the files manually before opening them in SNAP, according to the following discussions: