The Uzumaki clan were destroyed purely because they were such a danger.
Their Life energy is off the charts, which is why they are picked to be the hosts for the tailed beasts. They have incredible chakra pools, and i wouldn't exactly say "Sealing Techniques" are something to take likely...
Flying Thunder God is one of the most dangerous Jutsu's we've seen in the manga and it's just seals.
Death Reaper Seal is another incredible technique.
Edo tensei is another jutsu that requires seals.
Seal techniques are some of the strongest techniques that there are... If you're master of seals with incredible chakra and strong life force, then i would consider them to be incredibly strong.
I believe that we are going to hear more about the Ukumaki clan soon, and i wouldn't be surprised if they were considered the strongest clan!
Minato is a prime example of someone who was a master of seals, and look how dangerous he was! He never had any sort of "Boosts", yet he was an incredible ninja that relied on skill alone.