"Senden bile iyi."
Translation:Even better than you.
It cannot be "they." If you exclude "onlar" you must include the plural suffix to show plurality.
Otherwise, yes, you are correct.
"daha" is almost always optional in Turkish when you are doing a comparison. :)
So if you use an adjective with a noun in the ablative case, then the whole construction is considered comparative?
Even if you do not change the adjective in any way?
This is a comparative sentence. The comparative of "good" is "better."
"She is good than you" does not make sense in English.
I would say in principle it is the 'senden' which makes the comparison. 'from you' means / becomes 'than you' in comparison.
It's not as obviously to see the comparison as the adjective 'iyi' does not have comparative form which would be 'daha iyi'.
'daha' is optional as Alex wrote.
I hope that helps a bit.