So on that basis you could perhaps travel via Westbury - though the wait for a replacement bus there is rather long, so it's not a lot quicker (2h 28m).
12:57 from Paddington (rather than planned 12:27) to Westbury, arrive there 14:15.
14:29 bus from the Railway Inn (service D1), arrive
Trowbridge 14:47.
Total - 1 hour 50 minutes, versus 1 hour 46 originally sold to you, though half an hour later.
12:57 train run by First Group
14:29 bus run by First Group
Ticket sold to you by First Group (a special / advance fare they set)
It would be totally reasonable for First Group to convey you on that 12:57 / 14:29 combo on what strikes me as a far closer product they provide than the much later arrivals via Swindon (change and wait) and Chippenham (another change). It might also be good for them to offer you compensation for the delay of between 30 and 60 minutes on the resulting service - but careful what you wish for, as that may put them off selling the good-value advance tickets until close to the time, or at all.