Engels was quite brilliant in his own analysis and writing by himself. It's why Marx sought him out. It's just Marx was well Marx. It's a big intellectual shadow to be under. Like Lenin and Stalin from a theory perspective, Stalin is good at writing and explaining complicated topics but Lenin is Lenin.
And Marx and Engels were pretty much in complete agreement, I forgot the line but there's one letter from Marx which is like unless specified assume Engels and I both think this in all my writing. And a lot of Marx's writing surviving is because of Engel, he pretty much wrote Capital Vol 2 and Vol 3 from Marx's notes (Brandon Sanderson style) and published a few other books of Marx's before and after his death.