Is it better to invest in the entire market or wait to buy in ETFs for certain sectors?

I've been told and have read in countless investing and stock market books to buy the entire market using VOO and SCHD and that is all I need to do. Just literally every paycheck or every whenever put in as much as I can and keep buying. If the ultimate goal is to make money with as little risk of possible this may in fact be the way. However is it not better to buy not every paycheck or month but instead buy only when the market is down say 8% for the week? We have those weeks at least 3X a year it seems and that might be the way. The only counter to this is that if you are in a bull market and wait for the 8% dip you will eventually get the 8% dip. It may be after the market has ran up 20% though so you lost out of those gains.

Is it better to invest in VOO and SCHD or is it better to buy up sector ETFs? Say energy is the worst performer of the last 18 months. It is bound to start going up again, right? So why not invest instead of in VOO or SCHD but instead only in ETFs looking at sectors when they are not performing well since almost all sectors do well over the mid and all do well over the long run. The only counter I see to this again like above is you may be missing out by not being in the market long enough. If you instead just invest in VOO and SCHD you will come out ahead unless we have a major recession or even depression (and at that point I'm stocking up on canned goods and buying shelter equipment). If you wait until say energy is down to the worst performing sectors then you will loose out by not being equally in all areas of the market… So long story short I think the answer is to just buy VOO and SCHD and go from there. I don't even recommend buying individual stocks anymore tbh. The only exception to this is AST Spacemobile bc I see ASTS going up another 200% over the next year and that could make $10k turn into $20k+ very quick. I also believe NVDA is going to keep going over the next 3 years. Heck even if we somehow have a recession I think NVDA by late 2027 will easily be 2X from where it is right now. People saying to back off it right now are crazy.