In their implementation they choose to ignore RRDB documented parameters for conventional channels so you get multiple entries of the exact same thing in the programming resulting in poor performance.
You have it exactly backwards. The whole point of OFT is to AVOID poor performance by not scanning the same frequency repeatedly with various permutations of slot and talkgroup settings. Which is exactly what happens when you scan conventional channels tagged with talkgroup and/or slot info. Programmed OFT, a frequency is scanned once. Programmed conventionally, the same frequency is scanned multiple times--once for every combination of slot and talkgroup ID used.