If the premise of your question is that pilots from different groups within the seniority list have different objectives then by all means yes there are powerful conflicts.

You could argue that LEC reps then shouldn't be chosen just by base and seat but by some other more representative matrix.

Because it could be very dangerous for many pilots if those bargaining are in agreement with their particular constituency, say the negotiators or the powers that be are in the top 5% and they negotiate something extremely beneficial to them at the expense of 95%. Extrapolate that out to something for the top 15% but hurts 85%. Or, say the best and brightest negotiating team sits at 50%, and the 45-55% range gets something that hurts those above and below.

Now let's say the negotiating team is less nefarious than that but the TA offers is still basically the same lopsided result.

I'm not sure but maybe you and I are in more of an agreement than we know.