The ST1300 is, what, an 8-9 year old design ? Lots of tupperware (better weather protection), heavier, very hot in the summertime (makes the 03-05 FJR's sound 'cool'), less flickable, worse suspension that the FJR, OK but boring motor, basically a Gold Wing that hasn't been fed properly...
This coming from an ex-cruiser owner that loves his FJR after 18 months & 24,000 miles & a buck fifty on deserted Nevada highways, I have spent money on a Russell seat, Givi C46 top case, Wilburs, and lots of little things to make my baby 'perfect'.
I sat on the ST1300, listened to the salesman rave about Honda quality, and bought the FJR. Glad I bought what I bought. Sounds like your friend is just trying to get you to buy one to validate his decision to buy the mini barcalounger...
I checked the ST1300 forum (forget the address, it's been awhile) & the owners there, while professing fanatic alliegance to their mount, had way way more operational/build/parts quality complaints about their bikes than FJR owners do. Some of the problems were warranty problems that the owners couldn't get resolved, early parts wear, lube issues, some were flaky handling at speed, & some were just weird issues that seemed like an owner caused problem but probably weren't.
The ST1300 is an OK bike & if you want a small wing type of cushy no stress ride it's the bike for you. If you want speed, handling, good looks, good build quality & a company that stands behind their product, I suggest the FJR. Of course I'm biased. YMMV. No company / dealer connection, etc etc