Bought a new (old) house and a new subpanel for the pool was installed. No clue if this is safe
Junctions, done properly, are both fine and a fact of life; whether feeding a sub-panel or not.

While it's not the way I would have run it (because I've turned into a THHN/THWN and conduit for darn near everything person) nothing you have described sounds incorrect or unsafe. If the huge junction box were tiny there might be a problem, but it's not (you need some room to safely splice wires that fat.)

If you want persnickity opinions on details of the work, post pictures and they will get picked apart if there's anything amiss.