The biggest problem with a parliamentary system is that it can end up either of two ways-
If the ruling party has a majority, the prime minister is essentially a dictator for 5 years. The only thing that can stop him is if he/she gets carried away and does something sufficiently unpopular that their own MP’s rebel and turf him. (IIRC, isn’t this what happened to Thatcher?)
The other danger is that nobody gets a majority, and so nobody wants to make a tough decision. The ruling party has to make those tough decisions with the threat that at any moment there could be opposition parties who either vote against the government on principle or read the polls and vote opportunistically. A minority is often also a trap for the second or third party - if they are blamed for causing an election instead of getting along and passing reasonable legislation, they suffer in that election; so parliamentary maneuvering is often as much about optics and twisting the “political truth” as about actual government.
As mentioned earlier, the party whip keeps members in line. Basically, yes, you have to be into that sort of discipline to be in parliament. A finance bill, and any other bill the government defines as a confidence item, plus “motions of confidence”, a government MUST win. Otherwise, a defeated government must resign. If it’s been real early, technically the queen (or her representative, in Canada the governor general) might appoint the next biggest party to be government. In fact, it usually boils down to an election… Again half the election is spent arguing over whose fault it was that we are having a repeat in such a short time. But - because a wrong vote at the wrong time can trigger an election and possibly lose the MP his seat if his party is down in the polls, there is a strong incentive to toe the party line. Plus, in Canada at least, tax laws about political giving etc. are strongly biased in favour of the big political parties that designed those laws, rather than for individual politicians.
Finally, an MP is nominated by his riding organization (usually about 500 or less people have paid $10 to be party members, unless the seat is a hot commodity), rather than the public at large. IIRC it takes about 200 signatures and $1500 to register as a candidate. Anyone can run, and I have seen ballots that included up to 7 or 8 names, including independant and Communist Party of Canada (Marxist-Leninist). The central party leadership has to sign off on a candidate’s aprty affiliation, so again it’s a balancing act between the top and the grass roots - if a candidate is objectionable, the party can refuse to allow them to run as their candidate, but can stop them then from running as an independent. This could result in the independent winning anyways, or at least, splitting the vote so the other party wins.
IIRC there are about 630 members of parliament in the UK, vs. say 308 in Canada. I think of this as an advantage. In Canada, a majority is say, about 160 to 170 members. 50 to 70 make up the cabinet ministers, their assistants, committee chairs, whip, etc - all jobs handed out by the PM’s office. That leaves less than 100 members who are just backbenchers. maybe 50 to 75 of those are up-and-comers trying to behave and look good so that they might get the higher jobs in the next shuffle. Only about 25 or so realize they are going nowhere and being ignored for whatever reason to speak out against the party line and try to reign in excesses of the prime misinster and his ilk. (most such objecting is done in private, in closed caucus sessions).
In the UK, the same math - 350 in a majority, 60 to 70 in special positions, and say, 100 who hope they are on the ladder up - leaves 150 to 200 backbenchers who realize they are going nowhere and able to raise objections and dissent about party policy, to keep the party from implementing too unpopular a policy. Caucus revolts and real feedback are more likely in the UK.