Not really.. paid items aren't stronger than free items.

For example to get a new Warframe (your armor/character with unique abilities)

Free:

• Find/grind Blueprints for head, chest and legs
• Find components to build the parts (building takes time like 12h real time, you don't need to stay online/play the game)
• build Warframe (takes 24h real time)

Paid:

• Buy blueprints
• Find components to build parts
• Buy away the wait time
• Build Warframe
• Buy away the wait time

End result:

Exactly the same Warframe. You only need to grind less and wait less.

Every item/weapon/Warframe needs to be mastered. Either paid or free you'll need to play missions to level up your gear so you can attach mods to make it stronger. Mods are found in game or can be bought. Mods also need to be levelled up by gameplay to be better.

So in the end you only get the base stuff faster but everyone is required to play to get better.

Als some paid items are simply for more inventory space like extra weapon/Warframe slots. That way you can keep some more stuff instead of dumping/selling it to make room for new stuff.

To level up in Warframe it's necessary to keep using stuff you haven't used before. When you stay on your own gear you'll never really progress. But leveling up with new gear enables you to power up older gear as well.

And since it's mostly PvE you don't lose or miss out on paying players. If you solo stuff or are playing with friends then you're pretty much never in contact with a paid player.

If you play with random players then it is possible to have a higher skilled (either free or paid) player in your team that might make specific missions easier to do. But still that's totally up to you.

From all the F2P out there I personally believe Warframe to be the best game that handles their premium paid stuff without hurting free players.

The game seems complex, in the beginning it feel overwhelming. But don't be afraid to ask for help and search the Warframe wiki. The community is very friendly and the Wiki will guide you as well.