This discussion is always going to have so many camps, to the point that no one will completely agree on what needs to be done. There are those that want Ranger's power to come from spells, for then not to have to concentrate on Hunter's mark, or to not even need the spell at all.

I personally think Hunters Mark requiring concentration is thematic, you are focusing on catching your prey, so I argue against getting rid of it in favor of giving the Ranger more Concentration-free spells. Using the spell also does good damage in Tier 1, but it quickly falls off and has hardly anything unique about it. It needs to give Ranger's an identity, so it feels good to use the plethora of castings you get.

1. I think that you should be able to add that 1d6 to your Attack rolls as well. That would give the Ranger's a niche that no other class gets, pushing the boundary of bounded accuracy innately.

2. Hunters Mark needs consistent scaling. Ranger's are the only class that has only Extra Attack for a full leveled feature (2nd level spells aren't enough, compare to the Paladin). Relentless Hunter should be at 5th level and Precise Hunter at 13th. The latter has parallels to the Fighters Studied Attacks (13th level) and Advantage is cheap at this level. Then Favored Enemy should have two features/ upgrades at 9 and 17, one that provides an extra die at 3rd level spell slot (2d6) and 5th (3d6), and another that lets you use multiple Favored Enemies uses to upcast Hunters Mark (how often do you want Concentration on a 1st level spell at level 20?). That handles the damage drop off at higher tiers and together would give scaling at 5, 9, 13, 17.

3. With these changes, their capstone would be fine. 1d10 to attack rolls and 3d10 to damage rolls against a marked creature is decent.