An unfortunate setback to SCH is that we can heal, but as perviously stated, most do not like to. I personaly solod up to level 50ish, and took my role as a healer to maybe around 70. After that, I was mainly in manaburns with the occasional Mire party, but it was satisfying enough to be able to nuke every so often.
A piece of advice though is, build two sets of party gear. One for healing and one for nuking. Start to solo and look for party at the same time, and you will be invited to a party, most likely to main heal. This will give you the satisfaction of being able to nuke, while learning how to properly manage your strategems while main healing.
At endgame, it realy depends on two things. Your LS and your gear. If your LS is fine with nuking, then go ahead. Although, if you do not have the proper gear to land a nuke on JOL or any of the bad boys, then I suggest you support your party.
I myself, have convinced my LS that I can nuke properly and even out damage some BLMs. I do have a proper setup, while still lacking some key pieces such as the SCH AF+1 body and AF2 Hat. In the end, it depends on your style of play. If your realy dead set on playing as a nuker, I advise you to go BLM and give up SCH, as you will be a main healer more likely then not. Good luck though, and I hope you enjoy SCH as much as I do.