During the grind, it's extremely important to take some time to complete the story missions that lead up to The Second Dream and The War Within. Both story missions are pretty critical to the gameplay experience, and take a while to reach. That said, they open up so much more when you finish them.
Yeah with the updates they changed the sedna junction requirements, so I was able to do that and can do those missions now my Revenant is lvl 30 and complete the story.
If you're having th trouble levelinga weapon or frame you hate, go to Pluto and run Sechura to wave 10. It's the see facto leveling stage, mainly due to the ridiculous amount of XP you pick up. Hell, I was even able to max out my amp on there!
I was easily able to level things on ceres low level survival because it was increased melee kill exp, and I was using venka prime in that video and can shred through everything quickly, getting many more kills. Will look at harder survivals now I leveled revenant and also been recording a bit of fortuna.