Harô again anon o/ First thanks you for both your asks, I’m always open for any sort of Omegaverse question so don’t be shy ^^
And yes it is possible. Alphas being taller and stronger, Betas being average and Omegas small and fragile is just a generalization. All three dynamics have exceptions with a range of different body types, strenghts and heights.
If you want a practical exemple think of Dachi and Suga from Haikyuu!!. Most people put Daichi as an Alpha and Suga as an Omega. Daichi is 1.76 cm (5’ 9") and Suga is 1.74 cm (5’ 8"), it’s just a two centimetre difference. Suga would be considererated an unusually tall Omega, but he’d be an Omega nonetheless.
Or even another exemple Levi from Shingeki no Kyojin. Some people put him as an Alpha, others as an Omega (my case). But regardless he’d be an exception either way. As an Alpha he’d be smol :3 with the height of an Omega. As an Omega he’d be very sturdy and strong which is also unusual.
So don’t be afraid of writting/drawing taller and stronger Omegas or smol and not as strong Alphas, or even an unusual Beta that looks more like one of the other two dynamics (think Asahi from Haikyuu for exemple).
It’s true however that due to their biology it would be difficult for an Omega to be as strong as an Alpha. Since they have the capacity of having children they can’t change the fact that they’ll tend to have more fat than mucle mass. But hey everything is possible with hard work and dedication.
As for the gender thing, I think it has more to do with genetics than anything else. Maybe males have more of a probability to look more diverse since historically speaking they evolved after Omega females into being Omegas. But Genetics is a complex thing anon, so it can have a whole range of possibilities and outcomes. I still think that if you have a typical Omega mother (being them male or female) and berhaps a Beta father the chances of you being a unusually strong and tall Omega are low. It would depend on your family background and other factors.
But don’t let me saying that stop you from doing anything. This is just fiction. So an Omega or an Alpha can be whatever you want them to be.