Personally, I've grown tired of the design spam and liked BattleTech more when it had fewer 'Mech designs with more character.
Beyond that general grognard gripe, I don't have any specific problems with the Sun Spider, except perhaps that it looks as if it couldn't mass more than 40 tons. It's not ugly or weird, it just doesn't visually convey a 70-ton feeling; YMMV.
MWO canon is obscure. According to a ruling Randall Bills himself made, with Line Developer hat on, all Hero 'Mech fluff for MWO is canon for CGL's "core" BattleTech IP.
There is a Hero 'Mech Sun Spider, ergo the 'Mech is canon - that is, its name, backstory, and individual Hero 'Mech are canon. Its stats... only insofar as established by the fluff. By contrast, the MWO stats aren't canon.
The backstory marks this as a very obscure design - like many of my beloved BattleTechnology designs. The story isn't too bad; but it kinda sorta makes sure this design will always be a fringe design, too rare to make an impact. So ultimately, it's an okay design with little if any relevance. Nice, but unneccessary.
My 2 cents.