I put up with being a seal at a seal clubbing for a long while. Played Onslaught most of the time so that there was something I could actually kill.
Proving Grounds was a godsend as I had gotten to the point of needing to play my tier 4 fleet, and new tier 4 ships are nearly useless against seasoned ships with good loadouts. Over the many games that I played in Proving Grounds, I was nearly able to passively level up my chosen tier 4 ships to re-enter PvP. I was also almost to a tier 5 medium arty and gettin close on a tier 5 heavy arty.
Ran into one specific problem while in Proving Grounds. Somewhere about 14 kills the game usually nerfed my score. Getting 617 base points for 23 kills vs. 605 base for 14 wore thin quickly. Oh, and the other ships in your fleet got nothing. Greybox never did resolve this issue for me. Ended up playing most games watching my kills and then doing my best to find a corner to hide in while my team finished the game.
Then, one of the patches made the game litterally unplayable for me and I went elsewhere. I can play again, and I try a game every now and then, but don't find it near as interesting as my newer choice. I've probably played 4 games of Dreadnought in the last six months. I've got over 270 hours in my other choice in that same time and more ingame currency and experience that I really know what to do with. I also spent a good deal more real money there that I did here. Mostly trying to entice my kids to play with me.
For my money, and I did spend a bunch here, I'd suggest a good PvE environment. Proving Grounds is OK, but something with a goal that isn't just how many ships can you kill (especially when you effectively cheat your players out of their winnings). I got really good at that in Proving Grounds and it was getting old.
p.s. for developers: As I was transitioning from tier 2 to tier 3 I ended up playing ships that were already maxed out. Their xp could be converted for "gold", but I was 20-30 short of the amount needed. Rather than letting me convert what I had the "gold" to convert, I was forced to buy more. I think that was the last time I converted experience.