Spending money wisely wins you the league but most clubs aren't spending money wisely. Manchester United used money to win the league when they did in the past that no other clubs were able to compete with them. Chelsea came into the picture and did the same thing and won trophies after trophies. The next was Manchester city and they're still doing it and winning the premier league back to back. For Arsenal to be even competing with Manchester city for the title, they had to spend money wisely by acquiring players. You can't win without spending money. The reason teams like Brighton has been performing so well this season is as they spent money to buy players.
I agree with you that it is not only about signing players that guarantees you the league or winning anything. A clear example is when Madrid were signing the likes of Kaka, Ronaldo and the Likes of Özil but it didn’t work out because they didn’t win anything with that squad until they changed something’s. So yes I agree with you, that clubs can buy success if the players are signed rightly. But I wouldn’t say Manchester United bought success, because under Ferguson you wouldn’t see players been over bought or anything, moreover it is usually two or three non academy players you will see in the line up. This is because they played mostly with the academy players. Take look at the squad from 1999 to around 2007 it was majorly academy players.
The money tussle in the premier league started when Chelsea was acquired by Roman Abrahmovic and he went to spend close to 200 million and even brought Mourinho then who won the league back to back which started the rivalry and clubs started spending uptill now which brings premier league to been the highest spending league every transfer.