I have a question on the usage of Medisave.
Hitting the max MA does not appear to have much value to the account holder when their usage are capped by the medisave withdrawal limits.
Your predicate doesn't necessarily hold. In particular, see the chart Reddevil0728 posted above. When your MediSave is "full" (pegged to the BHS) you can do some interesting things with CPF to treat it like a weirdly high interest liquid savings account from age 55.
Assuming i have the top ISP , with or without rider, can Medisave that be used to pay for the co-pay and deductible portion completely?
Whether you have the "top" Integrated Shield plan or not, you can use MediSave dollars to pay for many medical expenses in Singapore(*) according to the various withdrawal rules and limits. (Whereupon you can often replenish MediSave funds, with tax relief, via Voluntary Contributions to MediSave. VCs to MediSave must fit within both the CPF Annual Limit and Basic Healthcare Sum.)
The Ministry of Health explains what you can use MediSave for
here. Also, upon the death of the CPF member, residual MediSave balances can be transferred to the member's CPF nominee(s). Meaning that MediSave can serve as a form of life insurance/bequest delivery if that's what you wish to do. And MediSave dollars don't have to be used for self. They can also be used for the eligible expenses of qualified family members.
(*) What about Singaporeans overseas? Well, MediSave dollars can still pay CareShield Life premiums, and you can still get CareShield Life benefits and MediSave Care withdrawals if you were to become severely disabled. Yes, even while living overseas. You can also return to Singapore for planned medical care that's MediSave payable, and very occasionally you can use MediSave dollars outside Singapore (in Malaysia notably if it's a MediShield Life eligible provider). If you're not in Singapore but have qualified family members in Singapore, you can still use your MediSave dollars to pay for their care and premiums (per MediSave rules). And your CPF nominee(s) get any residual. All of that still works.