The argument is whether an already competive club finishing around 4th to 8th needs those billions to win the league or if a world class manager can narrow the gap by himself.
Well if that's the argument this thread should be pretty short.
The league is a 38-game competition in which injuries and suspensions are inevitable. It is a marathon, it makes MASSIVE demands on your playing squad. You cannot win the league without playing all 38 games, and you will play all of the top six teams twice. Even if you save your best players for league competition only, and just field reserves and youngsters in the cups, you'd be unlikely to have more than three or four lads play in every game. The level of attrition is simply too high.
The cups by comparison are sprints. You can win one playing less than ten games. You might not face a top six side at any point, including the final. You could conceivably field the same starting eleven in every cup game, provided you are prepared to sacrifice a few league results to do so.
You CANNOT win the prem without a serious amount of money. Look at how much Spurs and the RS spend on transfers and wages... and they are both just aiming for fourth place! The teams above them (Manchester x 2 and Chelsea) spend way more. There are simply too many other teams in the prem spending a HUGE amount of money for any team to snatch a title with a smaller squad. Strength in depth is the key to winning the league.
The cups are a more viable target but the gamble in going all out for winning one is that you risk tumbling down the league table. The glass ceiling is VERY real when discussing the Prem, and no manager on earth can alter that. It is less of an obstacle in Cup competition, although it is not non-existent.
IMHO we are a starting CM, a starting RM and a starting striker away from competing for fourth place but, if we're prepared to drop to 10th or 11th in the process, we are genuine cup contenders as we are. To finish higher than fourth we'd need upgrades in every position because we don't have prem-quality depth anywhere.