Im gonna stop short of calling this outright nonsense, but it definitely borders on it. However, there may be another reason why using more than 7% of these is necessary.
First too tho.... VG does NOT mute flavor. I have been at 80%VG/20% everything else for more than a year and the juice I make is stellar and I use no more than .5% to 1% more concentrate than high PG users. Thats miniscule difference... and yes thats in batches of 60ml or more too. VG muting flavor, imo is a myth and anyone mixing correctly and vaping high VG will agree. I have tested this against pg based juices and there is no difference flavor wise except that pg tastes stale and vg is slightly sweet and makes more vapor, alot more.
Back to the OP. Maybe you can post one complete recipe and let us see what you are doing? Additives like em, lemon juice, ap, sucralose, vinegar can all do weird things to flavors if used wrong as well. The equipment you use can llay a role also. Battery voltage, atty, even whether or not the coil is any good matters.
On top of that there is the overflavoring issue. Dunno if you have experienced it as I have but you can... what I call... "double over" flavor many times. Hoosier's guide makes alot of sense when it comes to this. At some point too much flavor = no flavor. However, if you keep adding... it will come back... at some point.
My guess is it didnt work at 2.5% for the OP and then jumped to 5% or 10%... overflavored, didnt taste anything... added more... maybe even went past the sweet spot twice... to reach 25%.
Short of the op starting over and actually adding flavor in .5% to 1% increments then let em keep vaping SC's at 25%. Assuming gear and or additives are not causing a correctable issue... then for the op it may not be an error. Its still close to outright nonsense in my head but to each their own... taste is subjective... etc... etc.
Sorry i may have used OP wrong here... please read this as per the 25% flavoring post.