Warframe in the late game or even the mid game gets stale and that counting if you get through the overwhelming early game. In the late game Warframe is just not a but THE grindfest but WITHOUT any fun in it.

The average late game player experience looks like this:
>get a ♥♥♥♥♥♥♥* meta build for a warframe like Wisp/Wukong/Saryn with a ♥♥♥♥♥♥♥* meta weapon that kills the entire population on earth with a single trigger pull like Kuva Bramma/Nataruk/Acceltra or if you feel really braindead Ignis Wraith
>grind xp for Mastery Rank
>grind platinum to feel something by buying fashion
>repeat for 1k hours
*♥♥♥♥♥♥♥ as in drains any ounce of fun or challenge from the game because why try out a fun weapon/warframe/build if you can just genocide the whole Solar System by just pressing 4

This guide will objectively help you make the game feel fun, fresh and not like a waste of time.

If you want to feel even just a shred of fun in the game, consider the following:

1. uninstall
   
2. reinstall after a major update
   
3. play through the major update
   
4. realise that the game is still a snoozefest
   
5. uninstall
   
6. repeat for 10 years