Okay, so personally I had the exact same dilemma: choosing between modern and physics. In the end, I caved and chose physics- let's just say it's one of my biggest subject regrets. Of course, I chose it for all the wrong reasons, aka the supposedly very high scaling (though if you really analyse the raw data modern isn't two far off, in fact it is consistently one of the best scaling humanities) and the lack of memorisation (a big plus for me since I hate memorisation).
Those two reasons however, weren't enough for me to make it through this year (barely did) and if I could somehow turn back time I would pick modern. Of course, maybe I would've hated modern as much as I hate physics now. Let me tell you, if you have no genuine interest or passion in anything physics related (I recommend you look at the new syllabus and judge for yourself) , but you are considering it solely for its high scaling or for lack of a better word, laziness, then CHOOSE ANY OTHER SUBJECT BUT PHYSICS. Since you say that you like year 10 physics, you should be fine... though i would imagine it to be very different to the new syllabus.
What physics requires is true dedication and consistent practice, both of which come wayyy easier when you are genuinely interested in the subject.
ALSO YOU CANNOT CRAM FOR PHYSICS LIKE YOU CAN FOR MODERN AND OTHER HUMANITIES SUBJECTS
IT TAKES CONSTANT PRACTICE TO ACHIEVE HIGH MARKS
Also with the new syllabus, its going to be mostly calculations based, so I would recommend that you only do it if you are very confident with your math skills (mostly algebra).
Here are some pros and cons of physics (dk about modern since i don't do it)
Pros:
-not as much 'content' as other sciences (memorisation wise- even less memorisation with new syllabus)
-useful for engineering uni degrees
Cons:
-Can be dry (imo)
-Consistent practice required, can't really cram as there isn't much to memorise, you have to understand the material and know how to apply it in different situations
