Aside from the fact that the people who are unhappy are generally going to be the ones going into the forums to talk about being unhappy and the people who don't mind/enjoy the new mode are going to be playing it rather thank talking about it, thus skewing perspective on what the entire playerbase feels, I believe the progress nullifying bugs are really the biggest hurt on it.
I like the randomness. I like using frames and weapons I've forgotten about. What I don't like is getting six or more rounds into SP circuit, and having a bug cause all that progress to be lost.
Yes, there are always people who aren't going to enjoy certain things, but a less shakey launch would have helped keep things more middle ground so that the people who like the game mode also wouldn't have complaints due to it flat out not working at times.
The 'everything is viable if you invest' vs 'I am not investing in 100s of items I am not going to use' is an interesting look at how different people approach the time they spend on the game. You don't have to spend money/plat to get a weapon upgraded, since you can just spend time. I get why someone who doesn't have a lot of time to spend on a game in their freetime wouldn't want to spend time on something they wouldn't pick when they have a choice- especially when they have a choice 90% of the time.
Generally speaking, someone who has been playing the game longer is going to have a larger arsenal that is viably modded. They have had the time over the years to do that. They aren't going to suddenly be faced with a massive wall of 'oh crap I need resources', they've already got them.
Standard Circuit/Duviri, I can understand the loss of control complaint. I like it, others don't, it 100% depends om how you like to play your games. But everything is viable in standard mode, even without heavy investment.
SP- saying nothing is viable is actually just people saying, I am not investing my time in things I don't want to. I get that too, but this is a ftp grind game. It is designed so you have a reason to keep playing it. Which means they need something to motivate you to invest your time in. So DE said, 'your entire arsenal is up for grabs. Plus some other stuff'. Which means everything already in their game now has a use again if you want SP duviri modes to be easier. You just gotta like the game enough to put in the time. Or spend your money on trading for potatoes and forma. Fashion and convenience is their business model.