A few thoughts...
1) There is factually a growing database of successful
and satisfactorily utilization of the TSX in large DG calibers. This is a fact...

2) This being said, it is of bullet selection as it is of truck selection: there are diehard Chevy lovers, diehard Ford lovers, diehard Ram lovers, etc. (not to exclude the best of them all, the Toyota Land Cruiser

). We should expect that there will always be folks who distrust TSX, or distrust AFrame, or distrusts DGX Bonded, etc. This is also a fact, and so be it... And all it takes is one personal experience to develop one's own God-given Inalterable, Universal, and Exclusive Truth (you never get a second chance to make a first impression...)

3) My own experience has been with all three (TSX, AFrame, DGX Bonded) and Nosler Partition before that (.375 H&H), and all four gave me entire satisfaction. My own selection criteria is now not so much about bullet performance anymore -- all "premium" bullets, monometal or bonded, work (the 300 gr NP likely remains the best .375 load for Leopard) -- as they are about commercial loaded ammo availability, consistency of zero (i.e. not changing loads constantly), and, because I live in AZ Condor country where lead ammo is restricted, lead content. To make a very long story short I now use exclusively Barnes TSX ammo in 9.3x62 (wife's), .375 and .458 (and .470 before I sold my double, although I had a pile of DGS .470 loads for practice), and Weatherby TTSX ammo in .257 and .300 Wby

4) Regarding the .458 Lott, Barnes only offers the 500 gr TSX (and banded solid) in loaded ammo, so this is what I use, with entire satisfaction. Admittedly, I do not carry a caliper in the field to measure bullet expansion...

Nonetheless, I observe that the 500 gr .458 TSX is very long (1.663") and it digs deep into powder capacity, even in a Lott case (with a SAAMI spec relatively short throated Lott chamber). This has an impact on velocity. The Barnes ammo flies out the barrel at 2,200 fps specified (2,170 fps out of my R8 barrel), which is below the commonly expected (but rarely met, with Hornady and Federal loads being notable exceptions) 2,300 fps from a Lott
But curiously, the Swift .458 Lott 500 gr AFrame ammo (when available

) is also specified at 2,200 fps even though the bullet is significantly shorter (1.439"), so what is a man to think...
The Buffalo Bore .458 Lott load with the shorter 450 gr TSX (1.513") is specified at 2,350 fps, which would argue for the 450 gr choice, but I do not know at what pressure this load operates (Buffalo Bore loads tend to be hot...), so I do not know if we are comparing apple to oranges with the Barnes load, and whether the increased velocity is due to bullet length or load pressure...
All being said, 500 gr at 2,200 fps or 450 gr at 2,300 fps? Six of one and half a dozen of the other, whatever makes your boat float, and enjoy popcorn while the fervent partisans tear each others out
And TSX (and other monometal) or AFrame (or other bonded lead core)? Again, six of one and half a dozen of the other, whatever makes your boat float, and enjoy more popcorn while the fervent partisans tear each others out
Man it is a good time to be shooting .458's compared to the early bullets and powders...
