Yes and no. You can find the "premium" currency by just doing normal missions.

If you go out of your way to farm for it, saving up enough to buy the war bonds doesn't even take long. People speedrun low difficulty missions to maximize how much they get, and if you go into a lobby with high level players doing easy missions, that's usually what they are doing. It's faster with more people, too, since you can split up and clear the mission in like 10 minutes. People welcome additional players, too, as the super credits are shared to everyone, so no-one gets salty.

But mostly I've had enough to buy whatever catches my eye in the super store just playing normally. I've only grinded super credits once, for like an hour, when I needed a little more for the newest warbond. It was fun, even. Had a nice chat with the strangers in the lobby, and got a break from the sweaty high-difficulty missions.

And, nothing in the warbonds or superstore (armors aren't just cosmetic, they have buffs/debuffs) is universally more powerful than what you get without spending super credits.

If you just play using the base game equipment, you wont be underpowered compared to other players.