is 350mw vtx power really possible with the meteor65?
if i try to fly anything higher than 25mw, video cuts out when i arm, is this 1s system underpowered for 350mw video transmission?

I run my Meteor65 Pro at a maximum of 200 mW.  I think it will do 400 (or 350), but not necessary since I don't fly all that far away and in line of sight conditions, in which I also get a good video with only 25 mW.

I recommend you take a good hard look at your battery.  vtx works fine if you have a good battery.  "Good" means it does not sag very much when loaded.  The motors will do the most loading.  All 1S batteries sag a bit.  I recommend you check your battery, or get new ones.  Use a Vifly charger and make sure you are charging to 4.35 v (for LiHV, of course).

Even if your video cuts out you should still be able to read your OSD in your goggles.  What happens to the voltage level when you arm?  With a good battery it should go from about 4.2 volts to not less than about 4.0 volts when armed, but not yet launched.

The Meteor65 Pro does not have a current sensor, so you can't read current draw in the OSD.  That's too bad.  You have to focus on voltage.

Another obvious thing to check is the antenna.  Is it plugged in securely and not touching any other board components?

I think it uses the M03 VTX and yes, it will run at 350mW, but it will overheat rapidly unless you have the props spinning. If you are playing with using the higher power levels, have "Low Power on Disarm" set in Betaflight, so when you disarm it drops power back to 25mW or PIT, so you don't cook it.

For in house flying I wouldn't go above 200mW. 350mW is more of an outside flying type thing and 65mm is far from ideal outside.