Construction was supposed to be a gold sink. Then they add protean planks.
Summoning is supposed to be a gold sink.
Invention is more of an item sink.
Jagex has added other gold sinks: travelling merchant shop, the whirlpool at the deep sea fishing platform, Ritchie whom you can feed up to 10b in gp, boss instances.
Keep in mind, you can still do your own part by going around to shops and buying up runes and construction supplies and then flip them on the GE. Runes are profitable. But oh wait ... You'll complain that dumping 45m at the Keldagrim stone mason (another 5m if you buy reinforcing plates at the nearby armor shop) is a net loss.
Even 1 off sinks like the meylir clan potion recipes, giving 10m to get the door access to nex
So they do have gold sinks. Just players don't use them all. Or they aren't efficient.
Jagex could do something like just add a 50b and 100b to the Whirlpool for a new title (ie the trillionaire) or up Ritchie's cap with 1 or 2 new hats.
Other options are 1 offs. Like Making the loyalty shop outfits buyable for gp, or making the livid farm spells and bones to peaches just cost gp. Heck even if ALL minigame weapons, tools, and cosmetics were buyable for gp, you wouldn't solve the issue.
Problem #1 is Jagex keeps dumping in gold. New boss? Lots of gp/salvage drops. The hourly wildy flash events ... Spend 2 minutes in the thing, get 100 to 500k on salvage each hr. Tradeable resources with no alch value is 1 thing, but pumping in gold is the first issue.
That jagex hasn't nerfed it is an issue. They could do something extremw like cut gp across tge board for all pvm. But there would be backlash.
They could also,just punish all players by just removing like 10-25% of all gp, spirit shards, and salvage in all players possesion. Again, they get backlash.
So, jagex has few options to deal with the issue of gp currently in game. The GE tax is one of the few options avail.
What you also haven't done is suggest an appropriate gold sink. You complain but you,don't give a viable counter solution to the problem.
Also keep in mind that any "solution" takes dev time. Addimg a title that costs 10b or nerfing drop tables is easyish to do. Most anything else could take months.