Yes, you're right. But base salary is the only reliable number to use for comparisons. If we get into things like startup stock options, value is effectively zero on a probability scale. Monetary bonuses are paid out based on all kinds of factors that may or may not come to pass, and have their own taxes associated with them. The only reliable extra comp I can think of would be RSUs and similar at large tech companies, but those are already fairly well known.
In my industry bonuses are as reliable as public company RSUs. To my knowledge, there is less public information on RSU grants and bonuses so I am puzzled by your last sentence.