and that seems anathematic to progression in this game.
I would say that kind of gameplay, i.e sticking with only one thing is kind of anathema to games in general, I can understand the mindset because I have done it myself and depending on the game I will probably will do it again if I feel the need to specialise. As for Warframe, you can still specialise in one Warframe, one weapon and so forth. I have stuck to at least the one Warframe [Mesa] approach [plus I only touch Tenno/Orokin weapons] but that has changed because variety being the spice of life is true, if you don't experience the other things then you can miss out on something else that you would equally enjoy or more. I would suggest you give some others a try, you don't have to play with every Warframe or every weapon [you will have to get every one to 30 if you really want a mastery rank increase, which is why Hydron exists], not when Public is there, but just widen your horizons a little, instead of one Warframe have three as your mains, same with weapons. I myself have several frames that I touch above others, same with weapons really. Its always good to give yourself options, then you won't potentially get as bored. You can still have the one Warframe apparoach and add the extra bits to it when they come out [exilus etc] but for me that just leads to quicker burnout.
And as an extra about slots, Nightwave drops them fairly regularly and Plat is easy to make with trading, just sell a rare mod or two occasionally and you get all the slots you would ever need.
And holy shit I may finally finish off my pending Mastery Ranks:
Im MR 30 now, whoop whoop. Bow before me.