It is ok, that the rogue runs around with high stealth.Well in that case the rogue would just have a 20 on its stealth all the time, not that much less, and still how high than the vast vast majorities of passive perceptions out there.
I can say having run a stealth focused rogue in my game....I have learned two things:
- If the rogue wants to stealth they will basically be hidden, they will almost never fail.
- The key is to control when stealth works.... 5e allows for many circumstances where stealth just fails, doesn't matter if you have a 50.
I think where my reliable talent will be an improvement is in different skills like perception. There the rogue probably has a lower ability score, so the floor is quite a bit lower but still reliable.