a) scBTC have less value than BTC
If you are talking about a 1:1 peg I don't see this, really. If it persists then people will just flee the SC and it will become irrelevant (absent some short term uses like paying for coffee perhaps).
If you are talking about a non-1:1 peg then it isn't clear to me that scBTC need necessarily be worth less than BTC. For example scBTC could pay dividends in some non-convertable asset.
scBTC has almost same value as BTC (but there is little more risk. BTC == scBTC + riskOfConversion )
No the correct equation is BTC == scBTC + riskOfConversion - added value of being able to buy coffee with 1 second blocks.
The market will determine the difference in value. Given convertibility the difference, +/-, will be small or the side chain (or possibly the main chain) will be abandoned, at which point there is no theoretical bound on the price. (Convertibility in theory doesn't matter if you run out of coins to convert.)