Can't confirm that. Comparing vector maps without DB file, raw data ready for use with BC, and zipped for backup - I roughly get these values:

Topo Suisse V3: 308,000KB
Topo Suisse V4: 313,000KB

Topo Austria V3: 320,000KB
Topo Austria V4: 346,000KB

Topo TransAlp V3: 588,000KB
Topo TransAlp V4: 575,000KB

The only things I have noticed so far is that the V4's of Topo Austria and Topo TransAlp are missing bike/mtb routes, but both maps are newer! Topo Suisse V4 shows bike/mtb routes, colors have changed, but map seems to be the same, meaning I have not found any mayor differences yet.

Comparing IMG files or installers can be misleading sometimes, due to different compilers, copy protection, activation, etc.
If you want a rough 'guesstimate' about the information contained, zip the raw content because duplicate information is mostly neglected - this approach works with unobfuscated data only.