But, although, you basically rely on those full nodes to interact with the network doesn't mean that an SPV wallet is any less secure than a full node.
That is exactly what it means. How less secure your wallet is depends on the exact behavior of that particular piece of wallet software. If your wallet still connects to a variety of nodes and downloads and verifies all the block headers, then you can still achieve a reasonable degree of certainty that you are not being fed incorrect information. If however, at the other extreme, your lightweight wallet downloads absolutely nothing and simply asks a single node it is connected to for up to date information regarding your addresses and transactions, then you have absolutely no idea if the information you are receiving is accurate or not. You are placing 100% trust in that single node and its operator, which is obviously not secure at all.
Additionally, when you run a SPV wallet, your privacy might be compromised. You will be always requesting the same addresses to the same nodes, and if that node is storing that information he might link those addresses together as belonging to the same person.
However, I don't think this is a problem and neither a security risk for most users.
The most common way to use BTC is by using an SPV wallet, as few people really have the bandwidth and the storage capacity to run a full node (i don't have).