The fact you could make giant profits by buying from ge and selling to gen store due to jagex over-valuing item was obviously not intentional and therefore a bug.
People abused said bug and got banned for it.
There is no risk of being banned for playing new content - the only risk is if you are dumb enough to go out of your way to exploit something that is very obviously too good to be true.
Making big gains in short time is not something that can indicate ban.
1. Recently jagex relased new skill. Some people had 200m xp after couple of days, XP rates were abnormally high. No one was banned.
2. "too good to be true" is very subjective. For players with 10m gp: 5m gp/s is high For marchanter with phats and 2,1b it will not be as high.
3. Power creep is how jagex handle game. Every content is better than previous.
Just because you have previously been able to sell to stores doesn't magically negate the fact it was very obvious that it was not intended for players to be able to make giant cash stacks for doing nothing pretty much.
If something was 100% legit in past then players should be safe to asume it is safe with new content. Otherwise every new content could give you ban.
1) Invention is a tricky one. You could argue they should've done bans or a roll back quite legitimately but at the same time it does have some key differences.
First up being players sunk items and money into getting that xp, they weren't generating wealth from nothing so it does have a slightly different context.
Secondly being the aim of invention was to sink items and it did do that quite well.
Plus of course it would be a death warrant for the game if they went and banned half of the most high profile players and equally would really ruin invention (more than they did anyway) for everyone if they rolled us all back to day 1 once they spotted the mistake.
2) On no planet is paying a couple of hundred gp at ge and then walking over to gen store and getting 2.1k anything other than too good to be true. Especially when they item stacks enabling you to take pretty much as many of the item as u can possible afford in 1 go.
It was like 1000% return rate, that is too good to be true.
3) Power creep is a feature of updates, it is not a feature of limited time promotions designed to award a few cosmetics.
And no players should not assume making 1000% returns is legit just because you could previously sell items to a store.
If you went to a cash machine irl and it started spewing out all the notes inside it at you would you just take them all and go "well cash machines gave me money before so there's nothing wrong here"?
No, you'd recognise something wasn't working right and it shouldn't be giving you all that money.
By all means if you find old content that is giving you 1000% returns go nuts, it's been there and while and nothings happened to it. But when it's brand new content and it's giving absurdly good profits for not really doing anything you should be able to think huh, this probably isn't working right.