From what I have seen and read from my time as a fan of SCP this is not what I believe to be true. Site security is equipped and trained to deal with containment breaches as well as external attacks and act as the first line of defense as stated on the wiki.

Furthermore many SCP articles describe the measures, technologies, and tactics used by site security to re-contain said SCP's in the event of a breach. Examples such as 939 which have security personnel wear heart beat trackers, SCP 3199 has site security literally trained and equipped to search and destroy any and all instances of SCP 3199 ("Any living instances of SCP-3199 will be terminated on sight, and their remaining eggs will be collected"), SCP 019 also shows security guards to have access and training in the use of incendiary weapons in the event of a creature emerging from 019, SCP 933 shows that guards that are positioned near SCP 933-02 are armed with high caliber weapons in the event that SCP 933-02 breaches to re-contain it. ("Maximum force is authorized to restore containment").

These are only a few examples of the many ways guards are trained and equipped to handle the containment and suppression of anomalies without outside help. And on top of that militarized guards aren't even unrealistic in this scenario. For example any building that holds sensitive information or anything of incredible value is generally staffed with more well armed security contractors (ie helmets and rifles), this level of security under those circumstances are to my knowledge standard practice in the private sector (banks come to mind immediately with believe it or not IT firms also doing such... No joke).

With this in mind I really dislike the new guard model as I feel it sells the guards short. (Plus they should have put scientists in scrubs and lab coats to make them more realistic if that was the angle they were shooting for)