The creator of this website indicates on his note charts that +4o is not achievable, as does nearly every other website that comes up if you Google “diatonic harmonica note layout”. That includes learntheharmonica.com and bluesharmonica.com. That suggests that +4o is a skill not posessed by many people.
As “Slim” says at What exactly is an overblow? - #3 by Slim : “(That) makes playing them “on stage” a hit-or-miss affair – and for this reason many professionals never or almost never use them.”
Anyone who has mastered it is definitely going to have a full set of 12 harps including a G harp, probably multiple harps in other tunings plus various mics and amps etc, so I am not sure that reasoning is valid, but I do understand the blues sound concept.
PS. I am not interested in playing in anything other than first position and only on a solo tuned or chromatic harp, not a diatonic harp. I was just interested in understanding the concept as it applies to diatonic harps.
I am not alone. I have come across quite a few posts on various websites from people like me who simply want to play melodies on a harmonica and are not interested in learning bending or any other advanced skills.