
I'll be rude first. IMHO the idea of using an ABG as a transitional step to playing upright is nuts. A 34" scale ABG is going to play very similar to a 34" bass guitar, and I can't think of anything it does to help one develop the necessary technique and understanding to play upright. If the goal is to play upright, he should play upright. A full scale electric upright could serve as a proxy.
Totally normal. I have a Tacoma Thunderchief, which was one of the louder ABGs. Acoustically it makes a difference when I play, but it's not going to balance in the mix the way we normally expect bass to balance. Part of the issue is guitarist in acoustic jams often wank on their guitars to get as much volume as possible. IMHO, unfortunately the only way the typical ABG can balance with a couple of wankers on nice dreadnoughts is to use an amp.
Most ABGs sound more like the lower strings on an acoustic guitar than a upright. A big part of the issue is the Phosphor Bronze strings. I believe this type of string is chosen because they are loud. They have sort of a grindy quality in the mids.
My Tacoma sounds great through a small amp and has a unique voice. Acoustically it's pretty thin. The lows are full, bloomy, and clear with an amp. The Tacoma interacts with the amp quite a bit. At low volume this creates a really nice tone. But you can only turn up so much before the tone becomes uneven. If you continue to turn up, eventually the bass will break over into feedback. Less resonant ABGs tend to deal with higher levels of amplification better.
I believe a fretless ABG with tape wounds will sound more like an upright. I believe the tone will be darker and the volume will be lower.
Not sure how well intonation will be on a fretted bass with tape wounds.