Yep. Cheaper missiles in greater numbers will always overwhelm any anti-aircraft weapon system. It doesn't matter how expensive and sophisticated the missile system is.
Those who are developing relevant defenses, understand the significance of making them robust, capable and difficult to defeat.
A defensive system might feature 6 - 8 TEL (24 - 140 interceptors) and an FTR which can track over 100 high-value targets, and develop a fire solution for like half of them (25 intercepts possible, assuming salvo engagement for each target). The FTR might also be much difficult to jam.
You would need to strike at the defensive system with a minimum of 30 cruise missiles, or ballistic missiles, or a mix of both. This much firepower to defeat a single high-value target - cost-prohibitive I would say.
While you are at it, there might be additional set of defenses in the vicinity which might also attempt to soften your strike package. Therefore, you might need to expend even more to defeat the same high-value target.
Pakistan is a cash-strapped country with low defense budget. There are no cheap solutions for defeating multi-layered defenses incorporating S-400 systems. There is also the probability of the enemy to not wait for Pakistan to strike at its defenses first.
Russia is not doing Pakistan favors by supplying India S-400 systems. Pakistan would need to go back to the drawing board in regards to what to do next. Either China give Pakistan everything it have (which I doubt) or we exit from the costly arms race with India and declare LOC the border. Alternative is to transform Pakistan into an economic and industrial powerhouse which is a daunting task as well.
I agree with the view of PTI-led government to establish good relations with all neighbors; choice between prosperity (or) bankruptcy.
I say we continue to strengthen our defenses to the best of our capacity, but we need to think long-term.