Is that weak fire, weak cold and weak lightning, or is this another not-so-clear grammar issue?

If those are not all weak, may I suggest that we just plain list those in different order: cold, lightning, weak fire.

I think it was all three weak, yes. (Although I wasn't sure either when I first identified it, so I actually had to check they were all at the same level by comparing the damage per round to work it out.)

The description is clear, each property is separated by a comma. The convenience of not repeating the adjective each time doesnt apply to "code" text.

On a different note, I would remove weak brand alltogether and instead bind power to element:

acid x2, fire and cold x3, lightning x4.

Edit: Just to be perfectly clear, the reading is "Branded with <weak fire>, <cold>, <lightning>."

Great Rings of Power combo
 

I found this excellent combo of Rings of Power only after having found the one ring for the first time ever, so I haven't really had any use for them. Still, together they offer all four immunities and a solid set of resistances.

i) the Ring of Adamant of Tholdur (+4,+3) <+3>
Found lying on the floor in a vault at 5000 feet (level 100)

+3 intelligence.
+3 dexterity.
+3 tunneling.
Provides immunity to acid, lightning, fire.
Provides resistance to frost, poison gas, light, dark, sound,
disenchantment.
Provides protection from fear.
Cannot be harmed by lightning.
Speeds regeneration. Prevents paralysis.

When activated, it fires balls of electricity in all directions,
each one causing 150 damage.
Takes 441 to 594 turns to recharge at your current speed.
Your chance of success is 93.7%


d) the Ring of Fire of Impheb <+4, +1>
Found lying on the floor in a vault at 5000 feet (level 100)

+4 intelligence.
+4 wisdom.
+4 dexterity.
+4 constitution.
+4 infravision.
Provides immunity to frost.
Provides resistance to acid, fire, dark.
Provides protection from fear, confusion.
Cannot be harmed by lightning.
Sustains strength.
Slows your metabolism. Prevents paralysis. Sustains your life
force.
Radius 1 light.

When activated, it cures blindness and gives you telepathy for
9d9+24 turns.
Takes 246 to 300 turns to recharge at your current speed.
Your chance of success is 94.8%

I've never seen either of those activations before!

Second one appears to be the same as a mushroom of Clear Mind(?). No speed in either ring is about the only major deficit.

And the first is the activation on Razorback, a unique multihued DSM.

I find it amusing that the Ring of Fire provides immunity to cold. Curious how "Ring of Adamant" got generated though.

Nenya base item. The Ring of Fire is Narya, while the not seen here Ring of Firmament is Vilya.

So close! That should have been "Im-ho-tep".

Not Clear Mind, Second Sight maybe? Although if it also cures blindness I've never noticed.