Hi dixitraghav,
I'd be happy to clarify for you. Within GMAC's publicly released record of retired official SC questions, the preferred standard is clearly "consider" without any idiomatic partner word (such as "to be", "as", etc.) since the "to be" is considered less efficient.
That said, there is precedent for "consider to be", meaning it's certainly not grammatically 'illegal'. Even in GMAC's own instructions in the 2016 GMAT Official Guide, we find:
"
Try to determine how to correct what you consider to be wrong with the original sentence."
BUT, by the proven record of official GMAT SC questions, we'd expect the correct form of that statement to be:
"Try to determine how to correct what you
consider wrong with the original sentence."