Hiya, a few corrections:
Aero 1 was a DPS gain over spamming stone as long as it went full duration. It was also instant cast and thus was worth loading up mobs in a pull in dungeons as your tank tagged them.
A lot of people don't realise but WHMs also had access to Thunder which was a similar deal to Aero, full duration? DPS gain. Yep, WHM used to have 3 dots right from the start of 2.0.
You're also glossing over the depth added through our kit's utility. Stoneskin was an under appreciated part of WHM's toolkit back when Infirmity was a thing, and it was borderline required and needed very precise timing during early T5 prog to keep tanks alive.
Virus and Eye for an Eye were also massively important debuffs, enough so that T5 progression teams would organise a virus rotation for Death Sentence.
Fluid Aura was a god send for caster trash that didn't want to move.
But all these differences pale before the single biggest difference between healing in 2.0 vs now.
With top flight WHMs, it wasn't about the spells you cast, it was about the spells you didn't. In Coil prog it was routine to see WHMs winding up and interrupting Cure IIs to be ready to pounce on burst damage where needed, but conserve vital MP when it wasn't. It really does sting that hitbox is gone and all my Coil progression recordings with it as it was a very different style of play back then.
Was WHM better? That's open to debate. But was very different to how it is now. Much slower and more methodical. You had more brute force and weren't bound by cool downs like a SCH was, but you were almost entirely bound behind a cast time for the majority of your kit. You had to be so much more aware and alert as a result.