Wrapping does not diminish your staked ETH balance. Both your ETH and earned rewards can be reclaimed based on the applicable conversion ratio at redemption.
Each WBETH represents 1 BETH plus all of its accrued ETH staking rewards starting from when WBETH's conversion rate was initialized on 27 Apr 2023 00:00 (UTC+0). The rewards for holding WBETH accrued in the value of WBETH. As rewards are paid on the underlying staked ETH, the WBETH price denominated in BETH (conversion rate) will increase over time. Each WBETH will be worth more BETH.
Consequently, the WBETH price denominated in BETH is always larger than 1. That is why when you convert 1 BETH to WBETH, you will get less WBETH.
Example*:
On 22 July 2023, the WBETH:ETH conversion ratio was 1:1.01004105. When a user wraps 10 BETH, they would obtain 9.90058770 WBETH.
ETH staking rewards accumulate, and the user's WBETH becomes worth more ETH. Three months later, on 23 August 2023, the WBETH:ETH conversion ratio has grown to 1:1.01980774.
If the user redeems their WBETH on that day, they would receive 10.09669596 ETH, which includes both their staked amount and the earned rewards.
*The numbers above are for illustrative purposes only. The actual scenario depends on the conversion rate at stake/redeem, the holding period of WBETH, and on-chain ETH staking APR, etc.