No, Congress cannot "replace president at any time, and thus remove his title." Even by impeachment by the House, and subsequent conviction by the Senate, Congress does not "replace" the president, as if they had a choice in that replacement by naming a party to replace the convicted president. Not how it works. All Congress is authorized to do is to impeach, and convict. No verbiage exists giving Congress choice of replacement. Congress must bow to the presidential order of succession specific to vacating the office, Article II, Section 1, clause 7: the presidential office "shall devolve on the Vice President." Subsequent, lower level federal law offered a full list of succession, if needed due to potential incapacity of the VP.
No, it is not "even better that he didn't ask approval..." The president is not required to ask approval. If the president intends full-scale war, he must ask Congress. But, if it is a a limited engagement [less than 60 days] he only need advise Congress within 48 hours of launching the exercise. The president need not worry about the action "seem[ing] more legal" because his legality is set in stone already, There is seldom a condition of degrees of legality. That would be a condition of the effort to impeach, whether a president's actions rise to the level of "high crimes and misdemeanors;" a decision to which the House must arrive to proceed with articles of impeachment.
No, it is not "This specific war is a violation of international law which USA helped make and vowed to follow" because the ICC has no jurisdiction over the USA and never has.
No, it is not "where international law somehow applies to Iran who is defending itself, but not applying to USA illegal invader by international law" because, Again, the ICC has no jurisdiction over the USA and never has.
Therefore, your conclusion is a non sequitur.