I don't think SAMs are the problem here. If ASF are too good, then why not just nerf them? A proportional decrease in both HP and damage should do the trick (ie: reduce ASF HP and weapon damage by 20% each). If air blobbing is too good, then why not add more air-to-air and ground-to-air AOE in general? It seems like it would be a particularly good companion change to an ASF nerf too, since it would help against densely grouped air-to-ground units as well.
Regarding the concerns:
restorers are now way better vs air
janus spam will be dominant for longer
cruisers will be a lot stronger vs air
way harder to snipe a protected air t4 aftet you lost air
strat rushes are even stronger than right now address the above:
- Restorers currently seem too weak vs air anyway, so that seems like a good change.
- Janus spam can reasonably be countered mass-efficiently at the T1/T2 stage.
- Cruisers generally seem too weak vs air given their relatively high mass cost anyway.
- Air T4's currently seem too easy to snipe with air.
- It buffing strat rushes seems unfortunate but acceptable.