Our striker is also our best defender at corners

I’d decide whether his defensive value at the corner outweighs the cost of removing your best outlet. If he is genuinely your strongest aerial defender, keeping him in the box may be right. But then somebody else needs a clear job higher up or in the second-ball area. The outlet does not always have to be the striker. A quick winger can stay higher and threaten the space behind, which may force the opposition to leave an extra defender back. You can also release the striker earlier once the first contact is made rather than leaving him rooted near your goal until the whole phase ends. Practise the transition from the corner. The moment you win the first or second ball, who is already moving to receive the clearance? Set pieces create trade-offs. Use the striker’s defending if it is a real strength, but do not let that strength accidentally remove every route you have for getting out.