The manufacturer will almost always pick their own proprietary fitting rationale for their hearing aids over the standard rationales, because they think that their own rationale works best on their hearing aids. Otherwise, they wouldn’t bother coming up with their own in the first place.
The Personalization intake questions affects various settings inside Genie 2 but not the selection of the fitting rationales. The characteristics of the different fitting rationales is very subjective, so one cannot really make a hard definition of what the rationales are like in order to assign the personal preference to a rationale. For example, if you say you like bright sounds, how would Genie 2 know to if it picks NAL-NL2 for you that that rationale would be bright enough for you? What if you find DSL v5.0 Adult brighter than NAL-NL2 (which I personally do), and Genie 2 still picks NAL-NL2 for you? It’s better for Genie 2 to stick with VAC+ and increase the brightness control (the higher frequencies) gains than to arbitrarily decide which rationale is “bright” to your taste.
Note, however, that even if you have VAC+ in your default P1 General program, if your HCP makes REM adjustments for you based on an NAL-NL2-based target, then your REM adjusted gain result will now sound more like the NAL-NL2 rationale than VAC+, even though its base fitting rationale is VAC+ based.
That “can” be part of the reason why HAs seem to show to be “underperforming” when REM is done. The proprietary VAC+ (or whatever it is) rationale may not be designed to sound as bright as NAL-NL2 by design. So if your HCP tries to match a VAC+ based gain curve against the NAL-NL2 target curve, the VAC+ based gain curve may show to be underperforming in the highs compared to target, not necessarily because the Oticon HAs are bad and can’t amplify up-to-snuff per se, but it could partly be because the NAL-NL2 target curve is already stronger in the highs compared to the VAC+ target curve simply by the nature of its design.