adding a molex quick connect on a flipper coil?

Well what's the worst that happens when they vibrate off? You just reconnect it.
Not stupid, but pointless maybe? But hey what isn't these days.

How often do you switch out your flipper coil? maybe if game is on location and you have spare ones ready to swap in solder free it would make sense. Not so sure on home collection though? But its your game do what you want

HEP does it on all his builds. I’ve been adding connectors for coils and switches anytime I need to service something. Makes it easier to work on at the bench and to reinstall later. Haven’t had one vibrate apart yet

I put quick connects on all the machines I've restored, rebuilt or shopped. Then those machines go to the Northwest Pinball and Arcade Show for an entire weekend of play (many of them have been back multiple years now).

I've only had one incident where a quick connect has come loose. I tightened the contact and re-inserted it onto the coil lug and it's never come off since.

I've also had one coil burn up during the show (same machine I think) and replacing that coil on the show floor was super easy.

I suck at soldering at a machine when the playfield is vertical. On a bench (or table) I can solder just fine.

I like rebuilding flipper mechs on the bench too. You can position it where you want it and get that nice solder job your looking for. No risk of a solder glob getting on something on the PF somewhere else. EOS switches and caps can be put on more easily and neatly on the bench too. (For me anyway) I Molex most everything these days. Many different crimping tools work fine most likely, but I got one of these and it makes factory quality crimps every time. https://www.greatplainselectronics.com/proddetail.asp?prod=3132-CT&cat=89

I like putting connectors on the various assemblies. Makes it so much easier to simply unplug the assembly and take it over to the bench to work on it. This is especially helpful to do on Williams drop target units.