I guess we all have our opinions, and experineces
Everything I have read tells me that liquid yeast packs hold about half the yeast needed for a good fermentation in 5 gallons, the savoir for the guys using it is that yeast doubles every 100 minutes so it has the ability to fill out in 5 gallons before it really goes off. Lagers it is suggested to pitch twice the amount of cells as an Ale.
Now I always make a starter, I learned to do it early in my brewing days, it is a way to check the viability of the yeast I am going to pitch. If I am going have a problem I know before it is critical. now days with the availability of stir plates and flask it is just to easy to make one and kind of a no brainer.
My advice to you, and I give this advice all the time is to use a check list of everything you on when doing anything about brewing. I to this day still use one, and have added stupid steps to it over the year. Being in a hurry this last brew I did a few steps without referencing it, and missed adding whirlfloc to the end of the boil. So you see we all need the help, even very seasoned brewers. The thing that makes a good brewer a great brewer is the great brewer takes very detailed notes of each brew, or follows some, and he has check list not to forget anything.
You see, if brewing is an art, then we accept whatever happens, if it is a science then we can repeat a brew time after time.
where your brewing has become is where you decide to take it.