The
Valar are not really 'gods'. They are created beings, able to take various forms. Nor are they 'incredibly powerful' beyond all others. They are 'more powerful' individually, yes...but it is the 'mythology' of
Tolkien's work, not the reality, seeming to make them so tremendously 'all powerful'. Keep in mind they feared the
Numenoreans' great power and ability to wreak havoc and destruction in their own territory.
Yes,
balrogs were corrupted
Maiar. They chose to take a form 'seeming as a man, but larger'... one place noting 'twice as high as a man'. The reviews are somewhat mixed.
Other maiar, notably
Saruman and
Gandalf, took a normal (or even lesser) form (Gandalf appearing as a 'bent old man') in terms of size.
Sauron was a bit larger than a normal human or
elf, but not so outsized as people want to make him out to be.
But being essentially spiritual, to try to compare Valar or Maiar to those who can only be a physical form feels a bit odd.
Ents were beings inhabited by the '
spirits from afar' called of
Yavanna's thought. They stood maybe 10-12 feet high... so similar to a
balrog probably.
Of the choices given, the
dragon would clearly be the largest in 'size and height' as
Morgoth bred them to be so.
Speaking of Morgoth... (yes, he was a valar)... he was not only smaller than his
dragons, but smaller than
Ungoliant. He was not so large the gem in his crown could not be easily removed when he was put to sleep.
We give entirely too much 'size, power and height' to the Valar and Maiar as we do not recognize how exaggeration, enhancement and myth within Tolkien's intentionally mythological "former
ages" purposely blows them out of proportion.