First, many players who were likely to face little magic damage early would take the scaling MR glyphs to handle mixed damage more effectively after the laning phase. Second, not only did champions get the compsenatory stat buffs, but they also gained more AD or AP through traits throughout S8 that S7 runes offered in the first place.
Also, it's worth noting a lot of the old masteries were very % based IE 3% more dmg to low enemies, 1-5% damage increase upon killing enemies etc. It meant that snowballing was only marginally increased and didn't amplify early leads as much/ make polarised lanes any more polarised.
Second, let's take a look at some of the runes with direct analogues. Electrocute: higher base damage and ratios than thunderlord's. Coup de grace: 8% against Merciless's 3%. Grasp: up from 3% health damage to 4%. What about L: Bloodlines/Ravenous Hunter as compared to Vampirism? Or Swiftness (a rune which required significant investment into the resolve tree) against L: Tenacity which every AD caster and their mum is taking. Bandit vs klepto, Natural talent vs absolute focus, expose weakness vs PTA, Waterwalking vs explorer, Precision vs Sudden impact etc.
And yes, I know some of these are more situational, but I'd argue they're not situational enough to warrant the differences in power.
How about my favourite comparison, Feast vs Taste of blood. Remember when healing a flat 20 hp every 20 seconds was considered too OP so they nerfed it. Twice. And now we have a rune that heals 18 hp + scales with AD and AP every 20 seconds. And that's fine.
Gee whiz it's almost like Riot knew damage was high and allowed healing to remain as a band aid through ToB, Ravenous, and Conqueror. You can see that on a couple of their most of their champions over the past two years. Just a couple y'know, like Aatrox, Irelia, and Akali. And Sylas. And Yuumi. And Pyke. And Senna. And Aphelios.
I know people can come out with some stupid shit on this subreddit, but for Pete's sake, stop acting like there's zero stimulus behind this.