Show me a card game which is successful, yet doesn't receive multiple set expansions every year. You cannot, the business model is different. A card game must always introduce new elements because you don't have the mechanical mastery, so you must keep the strategy/knowledge aspect in the constant shuffle. It is a selling point, the idea that you will constantly encounter new cards and new mechanics. You will never find MTG players complain about the release of new sets, because everyone understands the positives of new sets. You might hear players complain about the quality of some cards, mechanics, calling some cards OP while other useless, but in general, a set is a huge benefit for the community. New sets keep the game alive.
What do new sets need? Staff, you cannot recycle artworks or mechanics, you must keep introducing new elements to the game, accompanied by the artworks, and sometimes even the complete stories or lore like MTG. Valve can starve CSGO or TF2 of content updates, because the game has enough mechanical mastery and player-interaction to keep it interesting. Valve has never spearheaded content in the game like other publishers, they will not be able to get away with 1set/year update model, because multiple card game developers have expressed that the golden numbers are 3-4 sets/year to keep the players engaged.
Cosmetics in card games are also harder to sell. Nobody has build a profitable card game monetizing foils/effects/avatars/card-backs. The weapon/character skins are more desirable than alternative-art or particle-effects cards. You can only show-off your items to the opponent.
Unless Artifact is going to be a loss leader, Valve will have to monetize the boosters/cards. CSGO/TF2/DOTA2 are NOT loss leaders, they have monetization models which net revenue, while the upkeep for those games is a 5-15 team of developers.
I think it is very clear that the initial package is going to be the starter pack and Valve has a full intention to monetize the extra cards/components to some degree.
