Yes that is too much thread on the bottom, it does look like the machine is not threading properly, make sure the top thread is in tension and also make sure the bottom bobbin is in correctly, sorry if this sounds silly but i cant tell you how many machines i have seen like this, check the thread is running off the bobbin the correct way for your machine, clockwise etc.
Could you try to wind your brother bobbins on your Janome, check that the bobbins fit on the spindle, if they do it might be worth trying if you are having trouble winding on the brother.
Can’t comment on the pre wounds as I don’t use them.