I equally agree, particularly as a Scholar player.
Because Crafts directly tie into Class XP - every class is encouraged to buy crafts as an easy way to increase their total xp not to mention round out the character to be more than just class skills. This has a universal encouragement - and with merchant having a direct tie to both buying/selling adventuring gear but monumentally important for CM. Yet Fighters, who are predominately Smiths - spend 30xp to get more use from that Smithing. Brewing and Inscription, which simply has a Scholar requirement - equally pays 30 xp. However Scounts pay less, and Rogues as cheap as Artisans.
From my perspective, something that is universally encouraged with intertwining interdependant skills... should be a flat xp cost across the board. Without it... Sylvan Rogue/Alchmyst/Merchant 2/Professions 10 - is just simply the "best" xp Build for both combat and crafting. Hands down - nothing else competes with it. Despite that Fighter/Smith/Merchant 2/Professions 10 (or Scholar/Brew/M 2/ P10) - should hold equal value and importance... because that was seemingly the method/reason crafts were tied to classes in 2.0's xp progression.
An alternative concept (adding my idea and the above idea)
M1 - Sell 500c
M2 - Earn 3 CM
M3 - Sell +500c, purchase upto 7cm, 1s/ea
M4 - The Adventuring equipment thing currently written (which I think should be reduced to 2s/cp, but maybe just me)
M5 - Sell +500c (maybe add more purchaseable cm, but at 2 or 3s/ea)
All Classes 2xp per level, Artisan 1xp per level
For me, as a 4column, Inscription x20 Scholar who is invested in various crafting/merchant things across multiple chapters. I would sell back a 9th level spell just to get the xp needed for this version of merchant. Its impactful & meaningful where I can honestly say having 5th level merchant is more important than being able to prison a 4th time. with an incentive of not being xp cost prohibitive. Whereas currently written - I don't know a single player who will be willing to pay 15xp for a skill which gives you the privilege to drastically overpay for adventuring equipment, you could barter IG to trade your wares with another player of the craft you need/want.