I practice Tac reloads irregardless if it has ever mattered in an actual gunfight. Why? Because it seems silly to me to finish a gunfight (or think it's finished) and continue to walk around with a partially empty gun.
I think if you have reason to suspect there are still active threats (even if it is a "lull"), any method to get the gun quickly topped off is sound. If you can tac-reload fast and retain the mag great. If you dump it, speed reload then grab it if you can, fine.
However, if you think you have handled all the active threats (all down, or ran away, or you retreated out of danger) and are Tac-loading to be cautious, it doesn't make sense to me to dump the partial on the deck and maybe break it or rack out a round already in the chamber.
I only have 2 reloads. Emergency where I always rack the chamber and a Tac-reload where I grab my fresh magazine the way I always do (index finger on the front-bullet tips forward), slip it between my index and middle finger when it gets to the gun, eject the partial in my palm and seat the fresh one, put the partial back in the pouch. It is very fast and easy to accomplish esp. since you aren't being shot at or anything, not sure why it gets made out to be slow and/or difficult?
I think IDPA gives the Tac reload a bad name/impression because it is an on the clock competition, so competitors are sprinting from location to location while simultaneously doing mandated Tac-reloads at hyper speeds where in real life you wouldn't be Tac loading there. You would be continuing to engage the known threats instead. Offhand, I have never heard of a prolonged civilian gunfight. So, you get into it with 1-3 bad actors, exchange gunfire then it is over in a few seconds. The tac reload truly would be after you think it's over because it is, you're doing it just in case. LE can get into prolonged gunfights and have but they are also rare.
In reality-as a civilian you would be shooting until it's over, if you hit slide lock in between, doing an emergency reload and continuing. After it's over, you can choose to do a Tac reload if you have a spare mag (or not, up to you).
From the perspective of how the mind works under high stress, the only way to have enough conscious control in a gunfight to count rounds is to get in enough of them that you can control your adrenaline dump/response enough to do so. Each time you experience an adrenaline dump and perform, you get better and better at it. The first time is almost all subconscious reaction based on training or fear/instinct if you don't have training. Each time after, you are in more control and can exert more conscious control in your reactions. The problem is, most people don't get into the 1 gunfight, much less enough to really get good at it!