Development is very predictable. An IFA asking for $7 mil to sign is going to be a major leaguer using just an average development plan (having him spend 3 seasons in the minors, moving up a level a season, having half way decent coaches, etc...) baring multiple injury setbacks, which happen far less frequently in this game than they do in real life.
The unpredictable nature of it, is you set a budget and you have no clue what the IFA or draft class is going to look like. There is no garuntee that when you spend the $20 mil max, you're going to see the best IFAs/draftees. I recently took over an old team of mine that had been run into the ground. The latest owner never bothered to show up after budget day, no coaches were hired, no free agents, team was worn down, etc. when I took over midseason. Despite a $9 mil IFA budget, I saw and signed the best IFA I've ever seen (at least in terms of asking price and current ratings, we'll see how he develops) while several owners w/ $16 mil + in their IFA scouting never saw him. Lucky me, sucks for the guys who had budgetted big.
You had plenty of options w/ that money. You can move prospect money as much as you want in a season b/w 6 & 20 mil. You could ahve used $14 mil to sign ML player or two, you could have used the cap space to take on somebody's expensive vet while they rebuild in exchange for a low level prospect. You also didn't get left holding the bag w/ your $25-$30 mil in prospect money the season before, you made a calculated gamble that you could use that money to sign a star, you likely passed on a handful of guys who could have helped your future ML teams hoping for a hall of famer. You made a gamble, it didn't work out. The last thing this game needs is more predicatability.