You can solo to max lvl now in a few days, a matter of hours even with the support of an endgame player. Either way the bulk of your time will be spent doing limit-break quests as opposed to grinding out levels. Once you have a some trusts (AI sidekicks) at your disposal you don't even need to buy gear for the most-part as they can support you way beyond the capabilities of a true soloist with perfect level-appropriate equipment.
Relics are easy enough to make to their basic form, however as they are in many cases outclassed by far more readily obtainable weapons before they peak out at the current 119(II-III) forms, to get one that's super-useful is still a significant grind. Simply put, although making a basic 75 relic/mythic/empy is easily soloable, that basically gets you nothing more than a nifty trophy piece. There's a ton more to do after that, and an additional, final, upgrade step is apparently being introduced around September's update.
The game's far more accessible and forgiving than it used to be for newcomers, the biggest issue is that after 16 years, population on most servers is spotty depending on play-times. They really ought to do another server merge, but I guess they are happy charging folks to switch of their own volition.