good enough, for now. Not good. What to fix, change, improve on ... only one right way which involves total replumbing. Other fixes merely reduce the symptoms of the true problem.
Overall your description may be clear enough for me to get the entire picture, accurately. I guess you have both a shower and a tub, and the tub drain goes under the 5' length of the tub to connect to a vented stack but not before combining with the shower drain first. Is that right?