This is not accurate AT ALL.
Supersonics/Hypersonics generally have to fly higher due to the extra speed, this is because the lower you are, the more dense the atmosphere is which means you'd have a lot more drag/resistance.
What this means is that you have a higher chance to be detected as there is nothing to 'hide' you.
Subsonics have the ability to fly low and close to the ground, using the terrain to mask their movement and the earth's horizon to limit detection time. I will attach a graphic that i have made for you below.
View attachment 759540
This is a VERY simplified example that explains what ive said above. Green being subsonic terrian hugging, Blue being Super/hypersonics. As you can see, the advantage of using the terrain to mask your signature will also give you reduced detection times, especially if you're in a hilly area for example, vs a flat area like the one i have drawn above. There's a reason why LRASM and NSM are subsonic, they allow for late detection due to their low flight altitude vs something like a BrahMos or Oniks.