For me I do believe the Apex is a better choice than the AT Pro. I did own an MX Sport - believing it too was a better machine (for me) than the AT Pro. Of course it helped that I had other Whites machines and was familiar with the way Whites machines operate.
I ended up selling most of the machines I did own (mostly Whites machines) and buying a new stable of machines. Part of that was because of the Apex - I like it well enough that I believed I wouldn't likely use the Whites machines enough to justify keeping them. I'm still in the process of becoming familiar with my Apex (the other new machines as well) but I've gone to my permissions with the Apex and pulled good targets (I've hunted those locations for years) out of a minefield of trash. Most importantly - the Apex is a lot of fun to use. I enjoy hunting with the Apex - and for me the hobby is all about having fun.
I cannot honestly say the Apex is deeper than the AT Pro, but I suspect it might be. I don't run tests with my machines - I just hunt with them.
I mostly hunt permissions with a lot of history (some dating back to the early 1700's). Those sites have tons of trash - bits of iron, square nails, pull tabs, etc.. The machines I own were chosen with that in mind - with a premium placed on unmasking ability. I chose the Apex as a machine that could hunt such locations, but also be a good choice for the beach (dry/wet sand) and parks - kind of a general purpose machine. My experience with the Apex thus far suggests that I made the correct choice.
My current machines:
Nokta/Makro Multi Kruzer
Nokta/Makro Anfibio multi
XP Deus
XP ORX
Garrett Apex
Tesoro Compadre
Vanquish 440 (my wife's machine)
Of those machines the only two that I owned prior to 2021 (and have quite a bit of time with) are the Multi Kruzer and the Compadre. My guess is that the two Nokta machines and the two XP machines are a bit deeper machines (than the Apex) if they are set up for depth. I'd also guess that the two XP machines are better unmaskers and the two Nokta machines are slightly better unmaskers (small coils and set up correctly). All four of those machines require more "work" than the Apex. The Apex is a lot deeper than the Compadre, but I'd guess that the Compadre is a bit faster. Both the Apex and the Compadre are fun machines - easy to use, easy to swing, and just plain fun.
The Vanquish is my wife's machine. I used it a bit while helping her figure out how to use it. I much prefer the Apex to the Vanquish - finding the Apex to be better in the iron trash and far more intuitive to use. I suspect depth is roughly equal (between the Apex and the Vanquish).
Machines I used to own:
Whites V3i - I loved that machine. The Apex is far easier to use; lighter weight and easier to swing. The Apex is not nearly as programable, but that isn't necessarily a negative. I think the Apex is faster (recovery) and unmasks better. I think the V3i was deeper (set up correctly).
Whites MX5 - I loved that machine. A very fun machine to use (like the Apex). The Apex is the more capable machine, with more options, yet as simple to operate. I think depth is roughly the same. The Apex is faster (recovery) and unmasks better.
Whites MX Sport - I think the MX Sport was deeper than the Apex. The Apex is faster (recovery) and unmasks better. The Apex is lighter weight, swings easier, and is more fun to use. The Apex has more options, yet is more simple to use.
Whites Beach Hunter 300 - The Apex beats it all the way... with the lone exceptions being depth and ability to hunt in water.
Fisher F4 - The Apex is vastly superior.
Teknetics G2 - The Apex is likely a bit deeper. Both are fast (recovery) and both unmask well. The Apex has a lot more options.
Teknetics Europro - The Apex is deeper. Both are fast (recovery) and both unmask well. The Apex is superior.
Garrett GTI 2500 - The Apex is much faster (recovery) and unmasks much better. The 2500 was deeper (all metal mode - with larger coil). The Apex is much easier to swing and has more options (frequency choices).
Minelab CTX 3030 - To be fair I just did not gel with the CTX 3030. The Apex is faster (recovery) and unmasks better. The CTX 30303 was probably a bit deeper, but I'm not positive. The Apex is far easier to use, swings far better, and is far more fun.
Minelab Etrac - The Apex is much lighter, far easier to swing, much faster (recovery) and it unmasks better. I suspect depth is roughly equal. The Apex is far easier to use and far more fun.
There are a few more machines that I used to own, but I can't recall them at the moment. At any rate - I prefer the Apex to them.
Bear in mind the fact that my thoughts may well differ from yours - and other detectorists. The machines I like most may be the machines that others do not like (and vice/versa). For me, the Apex is a good purchase. I am pleased with its abilities and believe it is a very good tool for my purposes.
As I gain more experience with the machines I currently own my thoughts on how the Apex compares may well change somewhat. While I do value depth, I place a premium on the ability to unmask good targets in a bed of trash - you may well have different priorities for your machine choices.