I think this take is on the cynical side. A more charitable interpretation would be what they say (but maybe I'm being naive): that they don't want to break the rules to fix what someone else broke by breaking the rules.

I'm not sure what you mean by "they consistently come up with the exact small number of Democrats needed to push legislation and bills that the party proposes to be against" -- if you mean the Republicans manage to get some Democrats to "switch sides" -- it's important to remember that this is how everything used to get done. Check the old votes: party-line was less common back in the day. And even now, Democrats tolerate members with differing opinions far more than the GOP does, and it shows in their voting patterns.