Using the method you have been will be ok up to a point. Same for BIAB. Up to a point, you'll be able to lift the pot (or saturated grain bag) to drain/rinse the grains of their sugary goodness. After that, you'll start to see the point of having a mash tun, with a ball valve and such.
Personally, I started my all grain brewing using the BIAB method. Problems I hit early on was limitations due to pot sizes to mash and sparge the grains. I then converted a cooler I already owned into my first mash tun (now owned by another brewer). That worked much better, but I needed something sized a bit smaller (the first was a 70qt Coleman Xtreme [green] cooler). I went with one of the 10 gallon RubberMaid coolers. That worked well for a time too, until I wanted to have the ability to increase the mash temp without having to try adding boiling hot water. So, I built up my current mash tun out of a keg and it does a great job. I can mash up to about 30-32 pounds of grain in it (good for most of my brews). I can direct fire it on my propane burner to maintain the temperature (as needed). I have it insulated too, so that's not really much of an issue (except in the deep cold of winter).
Try mashing 20+ pounds of grain with the BIAB method, without having another way to get the grain bag out of the pot/kettle (if you have a kettle, you should be able to drain it, but make sure the bag doesn't get sucked into the ball valve). See how long you can hold the bag up to get it to drain, or try squeezing that extra bit of wort from it.
IME/IMO, you'll hit a grain bill that will make you regret using the BIAB method for the batch.
BTW, I've never had really good luck with my vorlauf. So, I simply fit my boil kettle with the nylon grain bag I once used for BIAB and let the wort run through that. It catches all the grain particles that slip through the false bottom and keeps it out of the boil. I also get a really nice grain bed set this way (draining as far as the dip tube can).