Replying to the question: does 1 point Lightning Mastery worth spending:
If you want to run Countess in Hell Hardcore that 1 point is not enough - it will still be too slow and too dangerous
If you want to run Countess in Hell Hardcore EFFECTIVELY, I stongly recommend to build a Lightning soso: The build and the equipment can be the same, but dont spend points in the Cold Tree, only the Lightning tree: Max Light Mastery, Max Lightning (instead of Frozen Orb and Cold Mastery), and the rest can be put into Chain Lightning (you cannot max it, if you maxed Telekinesis and spent many points in Teleport, but it will still be very effective!) With this you can safely Blind-Teleport to the Countess and kill her very quickly - The only danger is if there are light immune monsters attacking you: Personally I restart the run in this case, you can try and kill her anyway but doesn't worth the time invested... Another advice: for Effective Countess runs 63 FCR is significantly slower than 105 FCR - it is negligable when running Meph, but reaching the Countess can be a much longer journey - I never use MapHack, so 9 frames or 8 frames Teleports are not the same! (Of course you can run other monsters with this Light Soso, Eldritch, Shenk, Summoner etc, but this would be offtopic... you can find info about it at various Light Soso Guides...)