I was thinking more of our typical politico/tongressman/governor/mayor in an area where they are recognized as such. In such a case, I think it would be obvious to everyone who the guards are and it doesn't make sense to me for them to opt for "concealability." Yes, their weapons should not be openly brandished. However, I don't think it would make any difference whether they have bulging belt bags/carry bags or whether the weapons are well-concealed. Everyone knows they are carrying weapons anyway.
To me, the situation is similar to that of drunks in a public place with their liquor bottles inside a brown paper bag. You don't see what is inside the bag but everyone knows it is a bottle of alcohol being carried by a drunk.
That being the case, why settle for semi-auto pistols? MP5 perhaps?
One word: Escalation.
You're describing goons, mystyer, the original, 1980's movie-kind and not professional PSD or Private Contractors.
Anyone who is REALLY trained in the art of close-in security or personal security will NEVER opt for a larger weapon unless the situation dictates it... why? Because bringing around very obvious weapon packs for anything larger than pistols may make you a "hard" target, but it also broadcasts your capabilities and firepower to the point that any dedicated attacker will know how to plan around or through your security to get to you.
Belt bags, unless WORN as they were intended to be worn(which is NEVER the case with belt-bag totting goons and posers), are a potential gun grab waiting to happen. What do you do if the opposition knows how to operate your concealment kit, grabs it from you during a diversion, and uses your own weapon against you? Boom. You and your principal are dead by your own defense mechanisms.
You NEVER BROADCAST your shots to the enemy. It's the same in PSD as it is in chess or basketball. You are basically always on the defense so you need to stay ahead of the game, and most of the time, the element of absolute surprise is so essential/game-changing that most, if not all trained PSD operators will go for the same.
You don't carry high-profile weapons concealed like the PSG's subguns unless your principal is equivalently high profile. If you can get by without raising red flags everywhere, then you have done your job the best way, and without even firing a single shot.
People who tell you otherwise and say, "Oh, you need to carry an MP5 or UZI or UMP for ultimate protection and to scare the baddies away..." are either talking out of their ass or don't know jack about real PSD work... unfortunately most of the time, it is also both.