Your best bet is to trait Signet of Inspiration and use both Wells and Mantras to heal. You can heal raids with just Wells but Mantra of Pain spam has become a thing so that is also a good healing option.
Mesmer does not have a truly good Heal specs which can be promoted rather it's entire kit is very situational. This leads only a few who can truly use in a support setting.
Alacrity Mirage and Quickness Chronomancer are the closest to a well established Build, hense them being much more viable options.