As others have pointed out - your numbers are almost certainly wrong.
Probably a combination of factors.
For starters, you say you’re using a Mag+ (magnetic resistance) trainer, but David K says that your current trainer setting in Zwift is ‘JetFluid’ (a fluid resistance trainer).
Magnetic trainers have a much more linear resistance / power curve than fluid trainers. What’s that mean?
Here’s the power curve for a Jet Fluid Pro:
I looked at your last race (WBR 1 Lap Volcano Climb Race). At 14.3 miles in 33 minutes, your average speed is 26 mph (just shy of 42 km/H). Looking at the curve you’re using (above) at that speed, your average (virtual) power in Zwift would be ~ 425W. This is in line with what you’ve reported above.
(stay with me. this is important!)
Here is the curve for a CycleOps Mag trainer on the highest resistance setting:
Notice that at the same wheel speed (42 km/H) the *actual* resistance you experience on your mag trainer is ~ 250W.
In short, you’re only doing 55.5% of the work that Zwift *thinks* you are doing because you have selected the wrong trainer type.
Put another way, you’re getting an artificial boost in power, and your in-game speed is unrealistically fast as a result. [edit to correct this] The advantage this affords you relative to your actual power output of 250W represents an 80% gain! [(450W - 250W) / 250W] * 100% = 80%
1000W+? It’s not remotely possible on your trainer. Look at the curve. At 60 km/H, you’re only at ~460W. Even if we assume the curve remains linear all the way out to 1000W, you’d be spinning at a ludicrous wheel speed of 130 km/H (81 mph). Suffice to say that your cadence would be *impossibly fast* even in your highest gear.
Another thing to consider is wheel & tire size. Is it set correctly in Zwift for your bike? The vertex comes in 29" and 26" versions. If you’re using a 26" wheel/tire and it’s set to the default 700c x 23, this will *also* inflate your speed (and, in turn, power).
Hope this helps, even if it bursts your pro-level bubble.
[edited to correct typos during calculations]