The old Solaris and Soul were more conventional (90mm stems, etc) geometry. The new ones (“longshot geometry”) are a similar principal to the Bird’s geometry.
The New Cotics are still very long/low/slack compared to most bikes, Bird just turn everything upto 11, to get anymore extreme you’d have to look at stuff like Geometrons and Sick.
Now depending on your POV the Bird is either the best geometry and future proofed against where the industry will inevitably end up. Or it’s an extreme bike that mere mortals won’t appreciate (and potentially still where the all bikes will end up).
Both brands have test bikes, give them a go.You might like the new style geometry of both but prefer some nuance of either.
IME the difference between a bike 5 years ago (like your soul) is that you can go faster on a longer bike and it remains stable. But it’s only better if your riding involves going fast for the sake of it of you ride somewhere where stability is a virtue (Lake district, Peak, Wales, etc). You can pedal them all day around bridleways too, but they kinda feel underpowered, like your legs are never going to match the frame. Unlike a more old-skool XC bike which can make even riding round a field feel involving! Even in the Surrey Hills you’ll find trails and rides that could suit either style of bike.