There is no risk of having your wallet drained, since you build your transactions and sign these via the frontend + you wallet extension. The node provider receives a signed transaction and thus can't tamper with the actual content, otherwise the signature would be invalidated.
The only risks that I could think of is that, for one, the node provider could scan your transaction and withhold transmitting it for some kind of front-running. However this problem exists even if your transaction is directly sent to the mempool and the node provider's reputation would be at stake.
The far greater risk is one that Vitalik mentioned in an interview (I sadly forgot where I heard him talk about this). It's that if everybody relies on external node providers, they have the power to silently update / fork the blockchain and you will have no choice but to go along with it. Vitalik mentioned that they could implement an upgrade that would, for example, give 5x rewards to all miners. Since you're not running your own node, you would accept this change by default.