And yes to the point about Regency romances. But even then, think of Austen. All the ‘friend ’ characters are there for a reason.
In P and P, Charlotte Lucas is there to provide semi-comic plot resolution to one of Lizzy Bennet’s wrong’ matches, to get Lizzy into contact with Darcy again away from her family at Hunsden, and to show us what happens when a plain, sensible woman ages out of the marriage market and wants her own home, but can’t marry for love. Jane Bennet’s ‘friend’ Caroline Bingley is there to facilitate/frustrate the Bingley romance plot — she appears to have no others. Lydia’s friend Mrs Forster is there to provide the invitation to Brighton which facilitates the elopement. Kitty and Mary have no friends because there’s no plot need for them.
The Bingley/Darcy friendship never strikes me as a natural one (proud, snobbish Darcy hanging around with very new money, only one generation removed from trade), but, otherwise, a proud, standoffish man of enormous wealth and good family wouldn’t be hanging out at a small town Assembly hall), so it’s needed to introduce Lizzy and Darcy. Similarly, Colonel Fitzwilliam is needed to give Lizzy information about Darcy breaking up the Jane/Bingley romance that she couldn’t have got elsewhere, and maybe also to show us that here’s an aristocrat who is also attracted to Lizzy, but tells her lightheartedly that an Earl’s younger son can’t marry where he chooses, hence another match she’s not eligible for.
There’s a reason for all these people.