I dont want to compare tsunade with other kages, but I'm sure she's the weakest hokage....
1) against Hashirama
no need to state reasons
2) against Tobirama
tobirama can dodge every jutsu of tsunade's, & can easily damage her.....so there'll be a loop sort of thing : tsunade attacks, tobirama dodges,tobirama attacks, tsunade heals herself...... however, eventually there'll be a limit to how much tsunade can heal, & thats why tobirama will come out the victor
3) Hiruzen: no need to give reasons
4) Minato : same as tobirama, but given the fact that he's master of seals, he'll end it sooner than tobirama....
& as far as achievements & feats of tsunade are concerned,
1) alliance with sand was due to naruto & gaara, not due to tsunade....
2) just as you're saying what minato did during kyubi's attack, would've been done without him being hokage, & thats not any special thing he did as a hokage, then same thing applies for tsunade....she'd have used her slugs even if she wasnt the hokage....
moreover,there were too many deaths, & that was averted ONLY due to naruto answering nagato's answer about peace......
3) raising the morale of leaf ?? as if other hokages demoralised everyone ??
4) rebuilding.....when she became hokage, the village was already stable, so she didnt do anything special, just continued the normal procedures a hokage adopts.....& about rebuilding after pain's invasion, it was yamato & others, she didnt do anything herself....
5) naruto's growth : Jiraiya was responsible for it,not tsunade
6) putting a special team to hunt down oru.....haha, oru killed hiruzen, after that tsunade became the hokage, so anyone would've put a special team in search for the killer of the previous hokage, nothing special done by tsunade here...
& last thing, she was not even the first choice for hokage, neither she was inclined towards the village....& look at former hokages, all 4 cared so much for the village.....
In short, she has done nothing special....as well as she's not as strong as other hokages, thats why everyone puts her last, & she deserves it..whether u like it or not.