Neph, the second proposal is just the old MT sealstone (or current one but with -33% changed to -50%).
As for the first proposal, see Dhyer, that's still just as much of a headache! Anyway.... to be clear, my original proposal in chat was actually the *reverse* of Neph's proposal above: get rid of all of the all-or-nothing "X% chance of this effect happening" because it creates massive scenario splitting and random chance, not make *everything* it. So something like Instant Death, Sleep, Petrify, Vanish, Reflect, etc. becomes single-target and works as usual. Damage, healing, and effects that obviously scale like buffs & debuffs get the percentage treatment. The only problem with this is when people disagree about whether something is "scalable" or not. I'm firmly of the position that something like Reflect is very clearly a special effect and makes no sense to "scale", so it'd stay ST. (Or, if we want to keep the current proposal, go ahead and make it 50-67% chance, but understand that match analysis will inherently become vaguer with "well if Yuna's Reflect doesn't get really unlucky, the team wins.")
Anyway, I'm mostly okay with the current MT sealstone as is. If you want a mild nerf + less headaches, I'd recommend the above, although that may be less thematic (since some things still end up ST).
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Re point values: FF1 Knight is pretty dang good at 1.0, FWIW. Probably not Dungeon-breaking or anything, but he's very solid (good damage! doesn't die! ID resistance!) and makes characters like Robo & Monk feel silly. Robo can actually probably go to 0.5, sure, he eventually the Ribbon for something approaching non-terrible Speed & MDef, and Vigil Hat + Crisis Arm for status-immune hax, but he's such a late bloomer. Even if he might be a passable 1.0 on Floor 6, he's just so bad dungeon-wise for floors 1-5 that he can use an even further price drop.
If you're dropping Ness to 2.0, DQ8 Guv can probably go as well. They're pretty similar (MT damage, MT healing, a tad slow) except that Ness is way tankier.