Actually, you can expect threshold power to rise if you performed strict classical polarized training comprised of easy/easy and hard/hard.
OTOH Xert is hybrid polarized by default. Work below TP is considered endurance level strain.
That also means “endurance” workouts will range from easy blue/aqua intervals near LTP to harder tempo/SS (green) up to TP (touch yellow).
You can steer Xert in the direction you want to go through your workout selections.
For example, if you’re time crunched you may prefer to pick workouts with more tempo/SS intervals when endurance work is suggested. Even so you’ll notice most endurance workouts that include tempo intervals move through “green” rather than hang there like traditional SS intervals (X% for X minutes).
To understand what qualifies as Endurance in Xert go to the Workouts Library and set Filter to Specificity = Pure, Focus = Endurance and Apply. Scroll through the workouts and note the thumbnail chart colors and XSS ratio. For Pure that will be X points for Low and zero for High and Peak strain.
Now change Filter to Specificity = Polar, Focus = Endurance and Apply. You’ll see intervals that push into yellow, orange, and even red yet the overal strain achieved is Endurance work. The XSS ratio will be predominantly Low but include High and Peak strain.
Lastly view the list with Specificity set to Mixed. Plenty of “hard” endurance work there. 
I’m pointing out these differences in case newbies are viewing this thread. It’s important to understand what’s different about Xert compared to other platforms as outlined in my Onboarding post.