Yes, it's true, it is not necessary to do any upgrades. The car will run just fine and in some hands may even be competitive. You'll find tho that many will suggest some upgrades. I'll go thru just a few and let you come to your on conclusions.
1. Aluminum steering rack or linkage. The kit one works fine till you "tweak" it. If you're a great driver that never "hits" anything the kit one will be fine. The rest of us will tweak it and be replacing it very frequently. It's much cheaper in the long run to add the upgrade.
2. Oil filled shocks. There may be a way to build the stock ones to work as well as the oil filled ones, but every time you adjust the ride height it's a rebuild.
3. Al front uprights. The kit ones will bend, the al one do not. Use the stock ones till you bend them then upgrade to the Al units.
4. CVD. Dog bones constantly fall out and get lost especially in crashes.
You get the idea. If upgrades are done for sound reasons, they are worthwhile. They will increase the "fun" if you're not constantly replacing bent parts, rebuilding something that could be adjusted with a twist of a collar and so on.
I really don't know how it is in other locales, but around here, all of the competitive cars have a number of upgrades.