She outclasses both hokage and sannin era in 1vs1 if your goal (and i don't see what other goal you may have if you use them in your team) is to endure eventually up to round 10.

Why is better?

Because since round 3 onwards, if you skillbroken her, she will land 3 standard attacks per round + 2 chases with critical boost (so you are almost granted to chaos whoever is in front of her, unless is immune, while also delivering to it 3 stacks of poison if you run water main every round) and she will heal your whole team TWICE per round (that means, most of the times, to almost surely letting your team wake up and get back hps on the 2nd application).

And last but not least, you have her 5 stars for free that means she is fatter and endure hits way way better than any 3star hokage or sannin era you may run.

Her mystery skill trials may be useful in specific lineups, but not in real immortal lineups. In that case you simply use the basic skillbreaktroughs.

P.S. Hokage is better than sannin with sbs in 1vs1 only if you use her with earth main and kurama naruto, but you need to use both and that the enemy don't run buff clearers, otherwise she is worse even here.

none uses her in 1vs1 simply because immortal teams don't stand a chance right now, regardless what version of tsunade you use, because too often you meet people with overstacked move 1 that wholly forgot what move 2,3,4 are + multiple ignition per round.

but the point is that wherever sannin war dies, also hokage and sannin era die, so... does it really matter?

(what's the point of looking at which tsunade you are using when you face agk or edo hiruzen blitz teams with overstacked move 1? Tsunade dies regardless in round 1 or at most in round 2 since she won't ever be your move 1. And what's the point of thinking about what tsunade is better to use when you face edo deidara + jinpachi or shisui + itachi anbu + fire main? You are so much ignited constantly that you never heal back 1 single hp).

So there's no point in looking at those cases.

The cases you have to look at are those where both the 3 tsunades survive after round 2.

Take the following team:

x x x

x Water Main Kushina habanero

Tsunade sannin war sakura cloak x

talents: 32332 or 32333, summon: eight bird, summon mystery: giant katsuyu level 3.

would you really put in the place of tsunade sannin war 5 stars full skillbroken one hokage tsunade or one tsunade sannin era 3 stars?