You are wrong, you are probably reffering to
MS Madara, then it may be true. Exactly MS Madara was equal to MS Izuna and when you saw
Tobirama killing Izuna you can say
Tobirama>Izuna/MS Madara, however even it could be debatable, as we didn't see all fighting but only outocome of battle with Tobirama killing Izuna by using FTG.
I mean it could mean:
1.
Tobirama was overpowering
Izuna throught all battle, meaning
Tobirama > Izuna
2.
Tobirama and
Izuna were equal through all battle, but
Tobirama has
more chakra(Senjuu), so he won
3.
Izuna was stronger but
Tobirama was able to
keep his own, and caught
Izuna by
suprise with FTG(Izuna was distracted, near blind or simply out of chakra)
In
summary, to say
Tobirama > Izuna as fact.
We have to see Izuna's techniques, Tobirama's techniques as well as who had stronger offence and who had stronger defence. All battle should be shown with showing all details, who was at offence, how long and who was at deffence and how long or maybe it was changing with each second one being supperior to other. We don't know unfortunetly, so until we won't see full battle of Izuna and Tobirama, nothing is confirmed.
Another fact that
Space Time Ninjutsu is tricky, it could even let much weaker shinobi defeat much stronger shinobi, who has much more chakra, sheer power. To fight against
Space Time Ninjutsu, you have to posses
special abilities to counter it, so it could let Tobirama or Minato
kill Hashirama/Madara, Sage's sons and even Sage of six paths taken by distraction if they don't have
special abilities to counter it. However it could mean
Tobirama/Minato > Madara/Hashirama/Sage's sons/SOSP ?
Answer is: No, It would be still
SOSP/Sage's sons/Madara/Hashirama > Tobirama/Minato, so if someone has means to kill you with one hit if you are distracted, it doesn't equal being
stronger. It could be but not certainly.
Only Madara's flashback showing
Izuna vs Tobirama all battle could clear this up and make it fact that
Tobirama > Izuna.
However for now, I can say
Tobirama >MS Izuna=MS Madara
BUT
EMS Madara(vote)>>EMS Madara(624 chapter)>Tobirama>MS Izuna=MS Madara
Tobirama will get his ass kicked if he is gonna face Edo Madara alone...
I am sure it will be like that:
Edo Madara vs Edo Hashirama, Edo Tobirama
Obito vs Edo Minato, Kakashi+-Edo Hiruzen
Juubi vs Naruto BM + All shinobi Aliiance+-Edo Hiruzen
Edo Tobirama wanted to go and said: "I will stop Madara" or something, because he wanted to protect Shinobi World, especially against Madara even if it could cost his life and him having small chance to none agaist Madara but it would be better than staying here with Sasuke and talking. It is very likely what Tobirama was thinking, or he may got some new power up/ability after Hashirama vs Madara, which could make him sure that he could take on EMS Madara, but I doubt it.
I am not Uchiha fanboy and I admit that Tobirama is strong but I hate when someone try to underate or overrate some character