100% agreed.
My bro in-lay owns/operates a body shop... he paints many cars every week. Multi-coat/pearl is easy when you're painting the whole car and even if you paint with the bumpers off... as long as you paint the car and all it's parts from the same gun same batch of paint/pearl mix. Problems crop up when trying to match pearl/multi-coat paints after the fact because there are two components to the paint, the pigment paint (white/red/etc.. ) and the pearl/metallic element. You have to experiment with test shoots (mix pigment+pearl, record formula, spray, clean out gun, move on to next formula, repeat..repeat..) till you get the correct pigment/pearl mix to match the car. I had a 2012 Pearl White Prius that needed some touchup prior to trade-in. IIRC my bro in-law tried six different formulas till he got the proportions correct. He always charges more when spraying multi-step paints because of all the extra work involved. There is pretty much no way a bumper can be painted off-site with multi-coat paint and match parts painted somewhere else unless you have really tight quality control.