This is the cover of the first volume of I'm in Love with the Villainess:

Looking through them, 3 of the 5 volumes have Rae and Claire facing each other, one has them standing to either side of their adopted daughters looking forwards, and one has the same pose the anime picture used.

Let's see, I'll use the very rigorous method of just scrolling through my library and seeing what different series do...

Adachi to Shimamura - pretty even mix.

Bloom into You: Regarding Saeki Sayaka - alone, forwards, forwards with the other girl looking at Sayaka.

The Executioner and Her Way of Life - these are all just Menou alone and also this is just yuri bait anyways.

The Magical Revolution of the Reincarnated Princess and the Genius Young Lady - most of these are forwards, but even though it's unambiguously yuri it's not really a good yuri story anyways at least not the early volumes I slogged through before I stopped reading it.

ROLL OVER AND DIE - the only two covers with the main couple have them looking forwards, and this is unambiguously yuri.

There's No Freaking Way I'll Be Your Lover! Unless... - 50/50 split, although this one's cheating because it's a yuri harem and scientific proof that the only thing harem series need to be good (if still trash) is to just be yuri as well.

That was just LNs too. Glancing at my comicrack library... Honestly looks like about a 50/50 split for the series that have tankobans with covers, but like half of the stuff I've got is just individual chapters. Conclusion: the assertion is in fact wrong lmao.