It is definitely the *safest* course of action, but not necessarily the best. In an optimal-world, games should create believable characters of varying sexualities, of course making sure to not rely on harmful stereotypes. Importantly, and this should easily be possible for a game with ~8 companions plus other "romance" opportunities (e.g., Minthara), there should be enough romance options to allow players of any gender/sexuality to have good options. This was a main problem for CP2077, which had 1 romance option for each combination of man/woman & straight/gay. No one wants to be shoehorned into a single option of anything.
Player-sexuality - while definitely the safest and most fair option - strips LIs of their sexuality (they can not talk about it or anyhow indicate. The good attempt was in DA2, when Anders had a special line for gay Hawk, but this is only one example I can think of).
I still do not understand why not take the next step and add sexuality for protagonist? You choose who your character is - gay, bi or straight - and potential LI reacts accordingly. A few lines changed depending on your choice would make the whole romance more believable, the existence of the sexuality will be admitted, and yet you would be able to get anyone you want.
