Thats not a great value indeed. But it also opens the door for some other weird scenarios and/or abuse.

Recently Amex offered an upgrade to FB Plat with a gift of 75K miles, as long as you stay member for 6 months. With this valuation those 75K miles equals 300 Euros, which is exactly the costs of 6 months Plat membership. Making it essentially free. And allowing one to get a card for 6 months, cancelling, waiting a little while and re-subscribing to do the same trick again. Meanwhile still banking those 30-60-90XP each time (Signup for free Gold, 30XP. Upgrade to Plat, get 75K miles & get 60XP. Convert the 75K into cash to pay for the Plat card. Cancel after 6 months... and have 90XP for free).

Of course 75K miles can get you a much better value (at least double, possibly triple) when spending it on flights. But now its actually hard cash... which does change things somewhat for some people.