Not quite. Chrome Time-style scaling can be outgeared by ilvl (it just isn’t usually because it only goes 1-70), so level 80 characters who any gear above ilvl 554 will likely be more effective, and ones who have like 590+ will likely be breezing through.
Likewise low-level characters will be fine for the reasons you stated. Also currently Timewalking requires a minimum level of 30 to 45 - presumably Chromie Time scaling will remove that minimum level.
The problem will be for characters in the mid levels up to just below 80, and undergeared 80s.
Right now, Timewalking makes insane XP for the mid-levels and up to 80, and drops gear good enough that going 70-80 in it makes sense. With Chromie Time those characters will probably struggle a lot. If most of the group is geared 80s, it won’t matter overall, but it won’t be much fun for those who aren’t.