I don’t disagree with any of that. I have the Sig MPX. It’s fun for what it is. I don’t have the round count you have. In my opinion it is a toy plinker. You just aren’t going to get the quality out of it that you will get with a premium PCP rifle. Same with pretty much all the co2 pistols out there, including the Sig line. If you have real Sig powder pistols, the co2 pellet sigs are toys but at least replicate the feel of their corresponding powder brethren.
Getting back to rifles, I have a Leshiy and the new semi Leshiy 2 is probably what you are looking for. Extremely compact. High quality. But expensive. You are going to need a good budget to accomplish your objective because you will also want a good red dot. If you are more wanting to practice dry firing to enhance your powder proficiency, I would suggest going airsoft gas blowback. The premium airsoft pistols and rifles are a lot less expensive ($200-$500 in most cases - you can of course spend more) and many function like a powder burner. I’m frustrated that co2 pellet pistols seem to have fallen far behind airsoft in terms of functionality and replica feel. Finally, although bulky and nowhere near replica feel or functionality, some of the PCP pistols are nonetheless getting more advanced in terms of accuracy, so they are also a lot of fun. Some are also very expensive but others like the Artemis PP700, 750 and 800 are very inexpensive and IMO great value for those on a budget.