True, if one wallet gets 0.2 BTC x 5 they will have 1 btc spread in five different places (likely for an HD wallet).
But if you spend 0.21 BTC two of those addresses will be linked.
https://www.walletexplorer.com
Wallet Explorer is free and can link addresses in wallets to give some more info.
Sites like coinbase pay for a more advanced version and get more info.