Froslass is base 110 speed. The argument is it's too good as a suicide lead. Let's see what in UU is faster:
Most of your arguments make no address whatsoever to the fact that if Froslass chooses to attack, it can safely ignore the Taunt and blow through most common leads.
Electrode: Taunts it making it's setup potential useless. 0 sets of spikes.
Ice Beam 2HKOs, starting the game off likely at 6-5 for the Froslass user while Electrode taunts.
Swellow: Pursuit 2HKOs, BB + U-turn will 2HKO, but Ice Beam OHKOs it right back, so it's not a good answer. Still, 1 set of spikes max.
Who cares? It's still a 6-5.
Alakazam: OHKO's with Shadow Ball or Psychic, can Taunt it. Ice Beam fails to OHKO. 1 set w/o Taunt, 0 sets w/ Taunt.
And you're implying there's anything in UU that ISN'T annihilated by Alakazam's Psychic?
Dugtrio: Can 2HKO with SE, but Ice Beam is an OHKO. 1 set max.
Again, your opponent loses their trapper. 6-5. And since when does Dugtrio lead?
Sceptile: Not a lead, but can 2HKO it with Ice Beam having a chance of OHKOing in return. 1 set Max.
Most Sceptile would come in and OHKO with Leaf Storm, assuming the Spikes. However, if Froslass has Sash (which she almost always will) she gets one layer and cripples Sceptile or two layers. And don't forget, she also learns Thunder Wave, which in most cases would be worse than Ice Beam for Sceptile.
Ambipom: Taunt stops Froslass cold, outsped and 2HKO'd with Payback or Pursuit. 1 set max w/o Taunt.
Froslass can ignore the taunt and 2HKO with Ice Beam itself.
Espeon: Speed ties with Froslass and can OHKO with Shadow Ball.
Froslass can't do much besides Destiny Bond.
All of this is not even mentioning priority or the fact Donphan is an excellent spinner to get rid of them. I'd say give Froslass another go.
Since when does bringing in Donphan on something that is capable of destroying it after Spikes damage almost 100% of the time constitute excellence?
MM87: While you're right about her being frail and SR being bad to her, she is still a levitating ghost and thus has 3 immunities to come in on, and with her speed and decent SpA, she can be a fine sweeper on a hail team and excellent Spin blocker against Donphan.
As has been addressed, she cannot Levitate. With Snow Cloak and Brightpowder, she can be a major annoyance/sweeper on Hail Teams if she isn't used as a lead. Froslass/Walrein in perma hail from Snover still pretty much laugh at the UU metagame in general when supported with good Pursuiters and Spinners.