The side kick has the following weakness:
- You will have one long leading arm and one short back arm at that moment. If your opponent uses your leading arm to jam your back arm, you will be in trouble.
- It's easier for your opponent to catch at your ankle.
The roundhouse kick is easy to be caught.
The front kick doesn't have these issues.
IMO, front kick > side kick > roundhouse kick.
I'd change the order for me and how I kick.
And I'd change the order again if I'm using the other leg.
And I'd change the order again depending on who I'm facing.
And I'd probably disagree with the arm references as to side kick weaknesses, but I'm not entirely sure what you mean...
Thing is, there's not one blanket side kick formula - I'm aware of (and practice) at least 4 variants (and probably 6+ sub variants) of tkd side kick - different 'chamber', different execution, different intent and different recovery. Also, different advantages and weaknesses that are entirely situational, and bear in mind the variants don't take into account how they're set up or whether anything else follows.
Same with a roundhouse - although I call it a turning kick, because a roundhouse is a turning kick variant. There's not just one type.