MSC tx is considered as spam. I am wondering if XCP have the same issue?
Yes, XCP is
blocked explicitly.
How does it work then if it's blocked?
Because Eligius only mines ~5% of Bitcoin blocks.
And no, BitSharesX is not a scam. I have followed the development of it for a long time. It is new code, not Bitcoin-based, and the delegate-based block creation process is probably the best implementation of a non-PoW system currently available (aside from "piggyback" coins like XCP). Daniel Larimer is a very smart guy, and he and the rest of the team developed BTSX in a fishtank, with frequent public testing, comments, and feedback. He was/is very active in the BTS forums and responded directly to a large number of suggestions, and implemented them if they were worthy. He communicated when he was switching tracks (he kind of painted himself into a corner with his originally intended way of implementing PoS, and came up with the delegate system as a substitute).
Perhaps it is too bad that the BTSX team raised so much money, but no, all "pre-mined" coins are not inherently a scam. If we set the bar of "fair distribution of un-mineable coins" at "100% fair" for Counterparty, then BitShares would get at least 75%. Their system was convoluted, but it was open, transparent, well-communicated and without any post-facto rule-changes.
Is BTSX "better" or "worse" than XCP? Impossible to answer. They both are very good in different ways. XCP lives and dies by its reliance on the Bitcoin blockchain. It is both a huge strength (maximum security, relative ease of implementation) and a huge weakness (slow blocktimes, complete lack of control over blockchain). BTSX has its own blockchain which is not hugely wasteful of electricity or any other real-world resource. It is super fast and responsive. Whether it is as secure as BTC will have to be shown over time.