@comeonnow0 For a contradiction to happen it would mean that the information is both saying why Excalibur is special and why Jandraken isn't despite showing the same features and being the same type of weapon, which the story didn't even confirm and you can see it by characters calling Excalibur an ego weapon but not Jandraken.
You're ignoring the characteristics shown for both in the story. The only thing they have in common: they are both sentient weapons.
Now their differences: for Jandraken 1/ seems to come from the scythe (the scythe is still there when he's manifested) 2/ uses his powers in his humanoid form 3/ seems to act only on the command of his master
for Excalibur 1/ is capable of independent actions in her human form 2/ manifest her powers once she changes in a sword (could use her powers by herself when she had a more mature appearance and was with God) 3/ depending on Heo Seoljin, she appears either as a broken sword or as a normal one
These are some characteristics you're ignoring because you're only focusing on the fact that they're both alive.
Even if the story shows them as sentient weapons nobody is saying they are the same type of weapons and there are enough differences shown to believe it. As long as you don't have an explanation, you can't say it's a bad story element or there's a contradiction because you have nothing to prove it.
No explanation doesn't mean it's a contradiction, it just means there isn't an explanation, it's as simple as that.
Also yes, Jandraken is weaker than Excalibur, I'm obviously talking about when Heo can draw out her real power and not the broken sword, you just have to look in this chapter.