No CB, no matter how good it is, whether the Cobra 148, or a Uniden/Realistic TRC-449, will ever perform like a Kenwood (or any other amateur HF radio). They're not designed to. They are designed and built to fulfill a price point in the CB market.
That said, they are an amazing triumph of technology for what they are. Modern CB design incorporates design techniques that are true feats of innovation. They make do with sparse and lean design and parts count that yet accomplishes excellent performance. No, they won't ever compare in IF bandwidth, and selectivity, or intermod intercept point, or transmit IMD characteristics, but they don't have to. What they do do, they do exceedingly well.
Clean up that Cobra 148, get it tuned up, and use it. I would not mod it at all, but leave it stock; it's worth more. If you insist on "extra channels" or higher power, just buy a good export rig, or better yet, use your Kenwood.