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I actually disagree. I have many HTs such as a th-d72, th-d74, th-f6a, and a ic Id-52a. All of which work just fine with either a digirig or a mobilinkd tnc3/4. All work with either the stock antenna, after market antenna or externally connected antennas ?

The Kenwood TH-D72 and D74 are the rare exceptions among hand helds in that they are actually purpose-built for data.? The RX-to-TX and TX-to-RX turnaround times are optimized for data to support the built-in TNCs.? I don't know about the others you mention.

You must have a remarkably clean unobstructed path to the digipeater or other station if the on-set antennas actually work for destinations more than a few miles away.? Or you have the western scenario of digipeaters on mountains THOUSANDS of feet above the users, yielding a true line-of-sight low-loss path over long distances. ? Or the digi is sited on a TV broadcast tower HUNDREDS of feet above ground level.?

Normally, any kind of? on-the-set? antennas are going provide NEGATIVE gain, due to the radio chassis being too small to provide a decent ground plane/counterpoise to the whip.? (On two meters, the radio chassis would have to be 19" tall to be a decent ground to the whip.)? The "rubber duck" or other whip may be tuned to match the 50-ohm output of the transmitter -- but the radiation pattern is mostly skewed up in the air? instead of straight out at the horizon.?? The only exception would be end-fed half-wave antenna designs which are 38" tall on 2M.?

FURTHER.....

Traditional 1200-baud packet/APRS uses audio frequency-shift keying of a single sine-wave audio tone. Simple AFSK can tolerate a lot of audio distortion and uneven frequency response in the TX and RX audio systems, and still work. ?

ON THE OTHER HAND...

VARA uses multiple QAM (quadrature amplitude modulation) audio subcarrier tones SIMULTANEOUSLY. This kind of very-complex wave form is FAR FAR less tolerant of audio distortion, uneven frequency response and over-driven transmit audio limiters in the radio, than the simple single-tone sine-wave modes like AX.25 packet or SSTV.
??? Audio Inter-modulation distortion (a.k.a. "IMD") in the TX and/or RX audio stages takes the original multiple tones and adds/subtracts them to/from each other, creating numerous additional audio frequencies in the pass-band. All this additional "trash" in the audio pass-band then makes decoding the original tones much more difficult.? Note that this kind of IMD can happen either in the transmit audio chain, or in the receive audio chain if levels are set too high.
??? Transmit audio level setting is very critical on modes like VARA -- You MUST keep the TX audio level low enough that no clipping or IMD happens in the TX mic amp and modulator chain. ??
??? (This is the reason for the complex "auto-tune" trial-and-error level-setting feature in VARA. If you have a communications monitor with a modulation scope, you don't need the auto-tune process -- you can instantly see if the audio wave forms of the transmitted VARA signal have clipped flat tops instead of a mass of smooth rounded over-lapping sine waves)