I do this. One drawback is that your overall family life fame is more limited.  So I now try to get most lifeskills up to professional on alts to build that up.

Another drawback is needing to travel more, since I don't have specialized alts in various lifeskill locations.  That takes more time and silver.  It is offset a bit by having a higher concentration of mastery in skills.  Also sometimes helps if I discover I need to use another lifeskill to support whatever it is that I'm doing.  No need to call upon a specialist alt or just making do with a sub-par mastery on an alt that has specialized in something different.

I don't use portals, I'd rather spend the time traveling overland/ocean.  A little of that is the expense, since I defnitely do not optimize my time, which also makes the opportunity cost of traveling less.  But most of it is about how I want to experience the game, which is also most of the reason for going with a true main.

But like you, I wonder what I may be missing by doing this, when it seems like most other players go for specialist alts.

Most arguments i see against it are:

1. Inventory blocked by other items, means weight / inventory slots are already filled by other items

2. Travel time, and no parking of alts at specific locations

3. Family fame

4. Buffs stop running on the respective chars until its used again, while if there is only one char, buffs will always run out

5. Specialised gear can stay on the char which means less swapping

The biggest downside you may run into is if you are tagged because you can not put any gatherable trade items or trade crates on mounts which really sucks, tbh with bdo in 2023 and how easy it to move trade items this should be changed but yeah.

I would keep farming and fishing on a seperate char but up to you.

I use to have all my life skills on my main which did PvE and life skills and i had my tagged char built for pvp when i needed it, this was good for a while till i realised how much trade exp and money i was losing from throwing them away. 

I think having your life skills on the same character is ok depending on how you want to go about it.

Having all your lifeskills on your main combat character, though, can be an issue because if you tag your main to another character, you can't handle trade items and fish, and tagging gets expensive as your gear is good.

I have 2 mail lifeskill characters, and then a couple that do just one thing, like a sailor, a barterer and a hunter, so that I don't have to worry about crossing the entire map when whales spawn, for example.

It's not that big of a deal though for any ocean content hands down Corsair is the way to go. 

23 characters are all minimum of professional with great majority Artisan in Cooking, Gathering, Fishing, Processing and Training. Season life skill buffs helps A LOT.

However, do have specialised Alts/main in the above skills who are at least Master in one of them.

AFK fisher stays at her spot. Guru 9

Cook stays in Velia Guru 4 Fishing Guru 24

Trainer Alt stays in Calpheon Master 2

Just measn that I save on cotumes and time, cause when I wanna do summat, an  Alt is there/thereabouts.