I'll try the simplified version. Equipment pieces gives stats, usually 3-4 of them. Celestial is an attribute prefix that spreads the stat points among 7 stats, buffed to 9 stats a few years ago. First a player gets to the point of equipping top-level exotic/ascended gear; sadly enough gamers are utterly oblivious and run leveling gear. Often times they will be recommended a Celestial build, as it's boon, tank, power+condi damage, healing but master of none. This popularity lengthens the time of big-group open-world event chains (plus semi-afk leaches during some events), and leaves them utterly unprepared for instanced content (skill level and statwise). If one calls this out in that section of the game, you will be anti-gatekept HARD, as one must always let people enjoy things.

Content-creator mightyteapot, among others, tried to rectify this amongst the community, but there is so much inertia to sail upstream against. These open-worlders are the majority of ANET revenue.