The equality here relates to feelings and the evidence of this is the rest of the verse:

(… فَلَا تَمِيلُوا كُلَّ الْمَيْلِ فَتَذَرُوهَا كَالْمُعَلَّقَةِ …) (…So do not incline completely [toward one] and leave another hanging. …): The inclination is of the heart as the Prophet (saws) said:

“O Allah, this is my division concerning what I possess, so do not blame me concerning what You possess and I do not.”[1]  

With regard to polygamy, justice is required. It is not permissible for a man to lean towards one wife and leave the other one hanging without divorcing her.

( وَإِن تُصْلِحُوا وَتَتَّقُوا فَإِنَّ اللَّهَ كَانَ غَفُورًا رَّحِيمًا … ) (…And if you amend [your affairs] and fear Allah – then indeed, Allah is ever Forgiving and Merciful): Note the affirmation by the two words: amend and fear. Fearing Allah (swt) (Piety) brings together all that is good, and amending is the healing of what has gone astray and the restoration of things to their rightful place. So, our religion forbids violence and demands kindness from man.

[1] Sunan abi-Dawood: Book of marriage, Hadith No. 2134.