I am pretty sure that who ever thinks Bretonnians are a fine team just has not played them enough and that he who says they are OP just has not played enough Blood Bowl 2 in general.
There are two reasons to "tweak" the Bretonnian team and the beautiful thing is that both of them can be achieved at the same time.
The first reason is to simply make them better. Right now Bretonnians can beat low TV Halflings, Goblins, Vampires and Ogres but fight an uphill battle against all the other teams. Why is that? It is because they have almost every flaw a team can have in this game other than "do nothing/something crazy on ones" like Ogres, Vampires etc.
-Low AV: having minimum 3x AV7 players on the field means that against a savy opponent that attacks those pieces first, Bretonnians are essentially a AV7 team untill they are down 3 players. Being AV7 is a flaw that is often used to even out some other advantages like with many elf teams and norse.
-Not fast: In a game of bashing, grinding, stalling cages, being slow and not being fast is almost the same thing= you are not fast. Not being fast is a flaw that is often used to even out other advantages like high str or AV like orcs or dwarfs. Fast teams like WE, Humans and Skaven do not have this flaw.
-Not strong: Having no player with str 4 or higher is a flaw that is often used in team design to even out other advantages like speed, agility or high AV. Elf teams for example have no str 4 but a lot of AG4 for example.
-Not agile: having no agility 4 player is a flaw that is often used when trying to balance teams that have great strength or armour like chaos and dwarf teams.
-Not cheap: Expensive players is a flaw that is often used to balance out very good teams like Necro or Elf teams. Granted, the Bretonnian linemen are cheap compared to other linemen but so are Grots and you don't see many people praising Grots these days. Being AV7 and AG2 makes the peasants horrible pieces, not worth 40k in my opinion as they cannot handle the ball, dodge away or take a punch. I would personally take 20k Grots over the 40k lineman every day of the week.
-Expensive rerolls: Expensive rerolls are a flaw used to balance teams with very strong positionals like Chaos Dwarfs and Necromantic. Bretonnian rerolls cost 70k, the highest price any team pays for rerolls in the game.
So what are their strengths? They must be many and overlapping to warrant so many flaws, right?
----> they are "jack of all trades masters of none"
No they are not. Instead of being able to attack your opponents flaws and capitalize on them like Hunan teams can do, the Bretonnians do the exact opposite and let every team they play play to its strengths. That is, fast teams get to outrun you, strong teams out bash you and agile teams outplay you.
--> The blitzers can win games all on their own.
No they cannot. 19/20 games I lose I lose cause I get bashed down to 4-7 players. No 7338 piece can dominate a blood bowl field by itself without Claw+Po+Mb.
--> They start out with some very good skills.
No they do not. They are an AG3 running team with no sure hands and 70k rerolls. Picking up the ball is quite hard.
They have 4 players with catch but no pass.
They have four players with Str access that all start with wrestle and so has little synergy.
They have fend on AV7 pieces that above all else must try not to get hit in the first place so fend is questionable.
--> They can foul very well.
Yes they can. Lots of Wrestle and 40K useless linemen makes a good fouling combo. Is that really this teams niche? Are you telling me that whoever made the final decision regarding the Bretonnian team design thought to himself "I am going go make a team of mediocre knights that have great fouling potential" Then please give them 50k bribes like Goblins. The rich, corrupt Dukes paying everyone off so that their teams can win fits the Bretonnian fluff and playstyle.
The second reason to tweak Bretonnia is exactly that, to better represent the Bretonnian fluff and backstory.
The best way to do both at the same time would be to give them some better armour. Even if only the linemen would get AV8 it would change everything; Even if only the blockers would get AV9 that would change everything; Even if only the blitzers got AV9 that would change everything.
Raising the armour of one positional has been done before in this game with good results. Giving the Bretonnian team more armour would fit their armoured knights fluff like a glove and make wonders for their competitiveness at the same time. As it stands, the Human teams have higher AV with AV8 accross the board and one AV9 Thick Skull piece They are also better at picking up the ball, passing it, dodging with it, can run farther with it, are better at bashing and are almost just as good at fouling as there is only 10k difference in their lineman cost.
Please give the Knights a fighting chance to find the grail by giving them armour worthy of Bretonnia.