If you want to be absolutely technical about the differences in strength:
-Ludoshel's combat ability is stronger due to possessing a power given to him by the strongest Goddess whilst having more experience in battle with a mindset that aids this, however, Elizabeth performs much superior in the magical department of power given her ark is much more powerful and versatile than his.
Obviously, Ludoshel is technically stronger because he possesses a very powerful magic ability, Flash, but if you took it away and looked at them both in an individualist perspective (i.e the power they achieved themselves, no influence from others) then they should be equal to each other.
They both have their strength's - so it's hard to say who is stronger than each other. Hence why saying they are comparable to each other is the better conclusion tbh
The PL's should be the same, just different in how they are allocated in each category (physical/magic/spirit).
And yes, at this point - there should be no confusion on who's ark is stronger.
Basically this to be honest.
Elizabeth is a ''glass cannon'' given how fragile she is whilst having insane magic.
I'm pretty sure he called her a ''soldier''?
And who knows, maybe Elizabeth had some character progression like Meliodas when she met him? The cursed lovers met on a battlefield during times of war, maybe Elizabeth did briefly participate in war herself?