If too much of a grind will remove players and no grind will bore them away, then the obvious thing to do is to hit a mid ground, have a grind, but have it be less of a grind. Make it feel like progress is being made relatively often. One thing that drove me away from levelling up my non STF character (Yeldur obviously) was the ridiculous grind from 30-35, it was slow and boring, and made me feel like no progress was happening. 35-37 was a whole other level but that's irrelevant in this particular case.
I gave up on it eventually and went onto my STF characters (Ladoea etc etc.) and now I actually enjoy playing them more than anything as I can play what I want when I want, if I want to play cav I just respec and do that, if I want to play infantry I respec and do that. (Or in this case I hop onto a different character as I have different characters for different things)
There shouldn't be a high level start out because that is what STF is there for, some people just want to hop in and beat shit up for a bit, then hop out. Skip the fun is an option that should be promoted to newer players which then gives them the option to choose between it, though, anyone in game telling them about the option should let them know of the downsides in that they can't level and can't retire to get loompoints and shit.
And as before, link the bloody players to the forum, if we get them here we can talk with them, ask them what they want. Talking to them is the best way to figure out what they like and want out of C-RPG and what would drive them away.