Thats all well and good until you go to brew your “regular” beer and find the mash tun is entirely too large and you have no depth of grain for your lauter.Equipment is the most expensive part of brewing. My advice is always: decide what the largest beer you want to brew is and size your equipment between 1.5x and 2x larger.
I have an Anvil Foundry 6.5 which has an 8 lb grain capacity. I normally brew 3 gallon batches. Yes that it is a problem when I go to brew an Imperial Stout or a barleywine. But I can always supplement those mashes with extract.
It’s a bigger problem when I go to brew a Scottish 70 with an og of 1.040 and find out for 3 gallons I only need 3.5 pounds of grain. Like I said, no depth of grain bed for the lauter and the wort never runs clear. I have to go up to a 5 gallon batch just to get enough grain for the wort to run clear. Not that its a terrible issue but I don’t usually brew 5 gallons because I don’t want to clean 50 bottles, sanitize 50 bottles, fill 50 bottles, and cap 50 bottles and then have 50 bottles on hand.
Bigger is not always better.