Lump sum for me is a good strategy no doubt, but it looks like it gives little room for discretion,
Nope, Bitcoin accumulation is based on your financial strength and availability of discretionary income. If you've a large discretionary income present, it's fine to lump sum since the funds are available. Personally, I wouldn't lump sum with everything at once. I'll like to divide the money into 3 parts, lump sum with the first part, use the second part to increase my aggressiveness in DCA and keep the last part for buying my target dip.
because sometimes i think an investor should be investing on a gradual basis since the investment is for long term basis especially bitcoin.
Lump summing doesn't stop you from buying on regular basis, it's always advisable that an investor has plans to follow up his accumulation journey by buying at possible intervals with respect to his cashflow even after lump sum. Lump sum is buying more quantities up front since there's a large discretionary income available at the time you got into Bitcoin and if your immediate buy isn't up to your accumulation target, then you're still in accumulation phase and should draw out plans to continuously purchase Bitcoin in order to arrive at your accumulation target.
Although some investors can decide to lump sum when there is a dip, but why not use the DCA method instead and increase your lot size hence you notice a dip.
Again lump summing in a dip doesn't stop DCA, like the investor from the description I gave above that has kept a part of his initial discretionary income from start for buying dips, he could continue with DCA and use the funds he already set aside to buy the dip when it comes by. Good thing you can still save up around 20% of your regular buy amount steadily for the purpose of buying dips and keep investing the other 80% into Bitcoin, so that by the time a dip shows up, you've enough funds to lump sum and get more quantities for yourself while your DCA remains not altered.