You are correct. Ender's extension (like all extensions) was all about getting control over his age 30 and 31 seasons, at the cost of guaranteeing money in his arb years. Folks seem to misunderstand how these contract extensions should be valued, considering the team already controlled the player cheaply for 6 years. There is almost zero value in paying a guy a few million less in his arb years after accounting for the increased risk in guaranteeing those seasons. Being able to dump a player at will is extremely valuable.
Was it worth taking on the risk of guaranteeing Ender's arb seasons to gain control over his age 30/31 seasons at $9M each? For a player who relies on defense to produce the bulk of his value...meh. Seems fine.
It's a perfectly good extension, and we deemed it as such at the time it was signed. Ender may be a 4th OFer with a pretty expensive option at the end of the deal, but he also serves as good insurance in case Waters/Pache aren't ready. If Pache/Waters is ready, they decline the option. If Pache/Waters isn't ready, they pick up the option and let Ender keep the seat warm for a few months before sliding to the bench as a very good 4th OFer.
Either way, I doubt Pache is ready to make Ender expendable by next off season, and I doubt Ender gets anything of any real value in trade by the time Pache does make him expendable. I'm higher on Waters than I am on Pache, and I think Waters is an Eaton-type of player...who probably also won't be ready to make Ender expendable this coming off season.