Tried Claris front derailleur and not impressed. Have FSA rings on one bike, and I am reasonably impressed--pretty much equivalent to Shimano 105 rings. I (as we all did) used square-taper for years and years and were much impressed with them compared to the old cotter-pin cranks.
Hollowtech is my absolute favorite non-pressfit BB system and according to engineers, is stiffer because the bearings are wider, closer to the load (crank/spindle attachment.) Can't say as I ever noticed a difference--except Hollowtech is a lot lighter .... but I am not, so spending money to save grams is silly, for me. Your mileage will vary.
Frame flex .... only one thing to change there, and that's the frame. But if all that is rubbing is the chain, and only on sprints .... not Too bad for a cheap-ish bike. Maybe ride less and lose fitness?
As for upgrades ... Definitely. Save up for a better bike.