Yes, converting Chase points to Marriott points is a bad deal.

For $10,000 spent at Marriott properties I would earn 200,000 MR points. 10 pts/$ + 50% Plat bonus + 5 pts/$ for using MR Visa.

200K points yields 5 nights at a Cat 9 hotel (180K points) total value $1800-2700 and 20K points left over.

It's always best to use points/miles in the program from which they were accrued. The only exception would be MR Hotel + Air Travel Packages combined with airline bonus offers, but that's another discussion.

While Chase/Chase Sapphire is good for the infrequent traveler, those of us that travel frequently use affinity cards associated with the programs we use and are most beneficial to us. I'm sure there are a lot better things for which to use Chase points than converting to Marriott points.

So to answer the OP's question, to a great extent it is you because converting Chase points to Marriott points is a bad deal, not that Marriott itself is bad deal. Actually Marriott has one of the best earn to burn ratios out there; but that's within its program.