There is strength and there is power.
Men are "stronger". Get over it. Women's hips are wider (designed this way for having babies). So their legs don't go as straight down as mens. For women, that angle gets compensated for at their knees which is simply a physically weaker structure.
I'm still a beginner in Aikido but this quote sends a red flag up in my mind.
Strength is a very tricky word. When I started Aikido I was very "strong" and could bench press a lot of weight, but I couldn't stand on one foot without falling over.
Doesn't Aikido teach a more holistic definition of strength that includes dynamic power, static power, timing, flexibilty, balance, and other strengths that are beyond my limited understanding? Are any of these are more important than the other?
Men might be inherently more muscular than women, but women are more flexible, which maybe you could make an argument that those are a wash.
What is statistically different is that men, on average are larger than women, i.e. the average of male heights is 5'8" whereas the average of female heights is 5'4". But does this difference matter, i.e. is mass emphasized as a strength in Aikido?
Just an anecdote from my experience - I'm a large guy but my female sempai has the best ukemi I've ever seen in my limited exposure, has the technique to easily overcome me during randori, AND I can't keep up with her in our warm up exercises (which include strength training components). I don't think gender has held her back at all. My male tendancy to value the bench-press type of strength did hold me back at first.