If that's the case, then you should include those generous contributions when calculating your set-aside fraction.

For example, if your employer matches dollar for dollar up to your 5% (or more), you would have 10% of your income going into your 401k.

Starting early enough, 10% can be sufficient. However...

When you assume an 8% annual return, it's important to realize that's before inflation. Historically, stocks have returned about 7%/year above inflation. Current expectations are calling for more muted real returns, so I'd suggest planning based on 6%/year or less real stock returns.

Finally, the above assumes your 401k is invested 100% in the stock market, which it may be. If it is, you need to have the emotional fortitude to stick with it through market crashes. If your portfolio is more diversified, say 80/20 with bonds, you need to reduce your expected returns further, to account for the lower real returns you can expect from bonds.

None of the above should be seen as saying you're in bad shape vis a vis retirement planning. It's just intended to give you a bit more realistic data to factor into your calculations.