I call BS on this.
I had the same thing happen, some of the stock Fender bridges are made of cast metal and are pretty flimsy. Started noticing my fretless jazz going out of tune (flat) and after about a month of dealing with that all the time it became VERY apparent that what was happening is the strings tension on the back of the bridge was bending it towards the nut. Granted, that bridge was off a MIM bass (I built the fretless myself) and all my other Fenders are USA.
I currently have three jazzes - my homemade fretless, a USA sunburst with a rosewood neck and a Geddy Lee. The Geddy came stock with the BAII. I put BAIIs on both of the other ones and hell yes it makes a difference - subtle tone difference (a little brighter), dramatic difference in sustain and harmonics. I'm guessing I'd have the same results with a different hi-mass bridge too. I also used to have a USA P-bass - the bridge on that bass was different than what came on my USA jazz (different vintages). The P was also a string through body or bridge bass, so the BAII was out of the question for that bass (as I preferred to string through the body). So, I bought a BAIII for it. Cool bridge in it's own right, but what I noticed right away was that the stock P-Bass bridge was actually heavier than the BAIII. After a couple of months I put the stock bridge back on and guess what? A little brighter, better sustain and harmonics. Sold the BAIII for more than I paid for it
Bottom line - it's subjective. Some people don't notice a difference where as I absolutely did, but just because there is difference doesn't mean you will like it. Sounds like your deluxe may already have a Fender hi-mass bridge, if that's the case, you probably won't notice much or any difference
Someone also mentioned that Fender hasn't changed their design in almost 50 years -- true - to a point. The basic design hasn't changed, but the implementation has, like going from 2 saddles to four, notched or "grooved" saddles and different, heavier material. Compare a new USA bridge to a vintage one and you will notice a pretty heft weight difference.
Someone else mentioned about having the grooves slotted correctly in a BA bridge. This is very, very true, although a lot of players that use BA bridges will tell you they don't need to be slotted - there is some truth to that as well, an un-slotted BA bridge definately has a different feel when playing. With flats on a fretless tonewise and feel wise you *might* like unslotted saddles on the BA better, but on a fretted instrument I doubt it. If you don't have the proper tools or knowledge to slot a bridge or nut you will want to have this done professionally. Otherwise, the BAII is easy peasy to install, and I've seen some newer BAs come with grooved saddles (not cut grooves, but like three grooves made in the mold for the brass - pretty cool idea, but I haven't played one).
They are relatively cheap and easy to sell if you don't like it. I've seen chrome ones go used for as low as $35, but average more like $50 - $60. Try it, if you don't like it, go back to original, that way you can see for yourself rather than taking the word of a bunch of (shudder) bass players on a forum. Everyone knows we bass players don't have a clue what we're talking about!
maybe i misunderstood.
