Not really. The problem is that with twice as many sigops, you would also have to hash ~twice as much for each sigop. Hence O(n*m). A problem known "quadratic

Not really. The problem is that with twice as many sigops, you would also have to hash ~twice as much for each sigop. Hence O(n*m). A problem known "quadratic hashing". This is solved by using a different way to hash the signatures that doesn't require full recalculation on each input. In Bitcoin Cash it is fixed for all transactions; in Bitcoin it is only fixed for SegWit transactions so an attacker could still do this, by not using segwits.