And thats it. That was one of the points I was trying to make. That cleric is not the backbone of any powerful build, but a small dip for some. Just like rogues.Cleric is amazing as a dip for heavy armor proficiency, shield/weapon profs and domain feature at level 1. Tempest domain is also part of the multi in some top tier builds.
Medium armor and shield is a pretty sizable AC difference especially since our dexterity will probably be 14 in this build (perfect for medium armor.) You could try a 1 level fighter dip on bard which would further delay your magical secrets and spirit guardians until level 7. Versus getting spirit guardians at level 5. Fighter/lore bard might be a bit better eventually but comes online later.
Another point that I was making. Yes for that very specific build you can find items and spec to radiating orb two levels earlier. And yet starting at lvl7 it will be weaker to continue. Besides, I never have less than 16dex on any character, including heavy armor wearers due to initiative being one of the most important stats in the game. Have a group of min 8 initiative characters (16 dex & alert , not even counting initiative bonuses from barb/gloom or items) , and group movement in the first round wins half of the battle already.
Heavy armor is definitely a big selling point for the cleric class. You can't just gloss that over. A full caster that can wear heavy armor and shield proficiency too. Cleric is most definitely not under powered. I was recently complaining about charisma based casters being OP especially Sorcerer and Bard. But cleric is better than wizard and druid imo.
Swords bard multis are absolutely broken to the point of making the game unfun. If you're comparing almost any class in the game to that it's going to look bad.
Cleric is underpowered in that there is nothing the class offers as a unique ability. It is only a dip for a proficiency that comes with some spells that "can" be useful. Druid is an excellent melee class due to tavern brawler, str based animal forms dominate early game and owlbear is quite possibly one of the best mid game melees one shotting even bosses with jump under specific conditions. Abjuration wizard's arcane ward is a build in itself, and portent die from diviner wizards is even more powerful than cutting words.
As for bard, yes it is the most powerful class in the game due to full spellcaster progression with either swords archer version ring/helmet spell DC combo , or with 6 lvl lore bard bonus spells. But lets take a look at other classes that impact combat with their unique abilities :
Barbarian Throwzerker : Even in honor mode without DRS, it is has the most damage at early levels. Not as competitive late game, but still a solid choice. Also no save prones.
Barbarian Wildheart : Tigerheart with wolverine aspect is hands down the best melee build in the game. Bleeding enemies are automatically maimed? A single source of prone, and anything not an undead/construct is out of combat, including legendary bosses. Combined with reverbration items, this build dominates encounters starting from lvl6 by itself and still very powerful late game.
Fighter Battlemaster : Lots of CC with either disarm or trip, bonuses to party members and very high attack bonus. 3 attacks per action is nothing to scoff at either.
Fighter Eldritch Knight : Best dps in the game with ranged builds, swords bard is only better due to CC options.
Fighter Champion : Only good as a dip, but the best dip for crit fishing builds.
Open Hand Monk : Second best dps in the game. Without illithid fly, would have been the best mobility class in the game as well. Incredibly powerful starting from lvl4.
Paladin : The smite mechanic is just incredible. While better as 2lvl dip with swords bard, base class still has powerful auras that justify going further.
Ranger Gloomstalker : Has so many uses in multiclassing either ranged or melee. Unlike assassin, this kit is also useful in boss encounters.
Ranger Beastmaster : Overall solid through leveling, abuses the entire battlefield at lvl 11 when combined with party blind immunity.
Sorceror : Metamagic. I find it extremely weird that wizards don't have access to metamagic in 5e. Also wtf with charisma to spell damage at lvl6? You can deal 700+ damage in a turn with fire variant. Either kill all bosses in a single turn (other than the two fire immune ones) , or kill a few enemies and CC others. Sorcerer is just bonkers late game. Also has access to counterspell. Like wtf
Wizard : Above mentioned diviner with portent is pretty solid. Combine with sorcerer for more power. While arcane ward is undoubtedly powerful, I just don't like the playstyle. Has counterspell.
Warlock : Eeeeh I don't like having access to only two spells per combat. Hadar is good, melee locks are not bad with the correct items either. Dips are pretty solid, has counterspell.
I look at all these kits mentioned above with their unique abilities, and clerics offer nothing thats stands out. Yes they are good dips for spellcasting builds for heavy armor + shield proficiency (which isn't always necessary) and thats about it. Maybe tempest cleric for storm sorcerer, but even that is subpar compared to fire sorcerers. Rogues are also similarly only good for dips, mainly thief for bonus action.