Wishy, first of all, as you've been informed, you don't have to bottom out any of the switches. The activation point is at 2mm, while they bottom out at 4mm (
source). Also, the difference in required force between reds and blacks is only 15g. Fingers cannot understand such a small difference. When it comes to keyboards, fingers get used to a specific amount of force through muscle memory after extended usage. Therefore, when using rubber-dome keyboards your finger learn to apply around 70g of pressure on the keys.
Pressing a key multiple times, like while playing osu!, consists of 2 different movements. One is a downwards movement while applying force and the other is an upwards movement while the finger's muscles are in a relaxed state. While a low force switch (reds) makes the first movement to complete faster, on the other hand, a higher force switch (blacks) makes the second movement faster. When coming from a rubber-dome to red switches, your fingers apply so much force on the keys that they don't receive the key's feedback, making the finger's joints to do a lot more work than they used to to lift the finger, which feels uncomfortable and makes the movement slower. In this situation, black switches, not only don't require more force than rubber-domes, but also they feel faster to press repeatedly due to the stronger feedback.
Ultimately, reds might be better than blacks in terms of speed after getting used to. However, they require a lot more time to get used to when coming from rubber-domes and probably they will frustrated the user at the beginning. It is completely logical for a rubber-dome user to be more comfortable with blacks than reds and actually feel the improvement that a mechanical keyboard provides. Even more, you may be able to make better usage of the reds after being already used to mechanical keyboards. You know, sometimes, the ending result is better when the procedure to achieve it is smoother.