Take one of those models- say the Kona Dew. This will be sold at a variety of prices from very cheap to "How Much"? The frame is the same across the price range- all That changes is the parts to bolt onto it. So in general- the cheaper the model- the cheaper the parts are that are fitted to it.
C series and I have no idea---Altus was second rate 20 years ago so is not fitted that often nowadays. Acera and Alivio are better but still not top rate. if you are looking for a group set that is "recognised" to be acceptable- then it will start at Deore on flat bar bikes and Sora on Road bikes. Neither of these are "Good" but they are acceptable. But these two groupsets may not be fitted as complete sets. A couple of tricks that are pulled is say an Alivio groupset fitted but a Deore rear derailler. All you see is the part you can obviously see. Or a Full Deore groupset but lower quality brakes and Crankset fitted.
You get what you pay for I am afraid. BUT- I can assure you that Altus did work 20 years ago and will work today. Acera and Alivio are definite upgrades so nothing wrong with them.
What I would be more concerned about would be the heavyweight handlebars and other components and the Cheap no-name wheels that are fitted to the lower cost bikes in a range. And that is something that will definitely be on a Wally Mart store bike
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How long was I in the army? Five foot seven.
Spike Milligan