Without knowing Bungie's network infrastructure, it might not be that simple. There could be multiple reasons why they can't get it to work in the current version of Destiny. On a technical level.
With all the rumours of how Destiny's engine is a pain to deal with, I wouldn't be surprised if the network code they have in place, for strikes, can't be expanded for Raids without breaking Destiny. Which could be why they never implemented it.
I highly doubt that for one reason. Back when weekly strikes were first introduced in Y1, they had no matchmaking. One week the added mm to them. They can surely add and subtract mm at a whim. Now as far as server browser goes, well that is different. But really how much different is it than joining your friends fire team? If you can select a friend from your roster and join them, I don't see any reason you cant select a random from a list and join their fire team. I have a very small amount of game dev knowledge and I don't think it would be too much of a stretch.
An in-game browser isn't a bad idea but it's not going to solve the issue of time. Allowing for parameters just serves to gate the content moreso than it is now. (LFM WOTM Normal LL400 must have previously cleared... Then you join to find the leader has LL 390 and never played the raid and doesnt know strats etc...).
This isn't just supposition. It's literally already happened a LOT in other games. This is why I said there is no perfect solution. It is *not* easy to implement a system for Raid grouping that has everyone happy. It's never been done. So it's really up to Bungie to pick whichever evil they feel best suits their game and hope it works out. Given that we're on Y3, and Destiny 2 is on the way, what they have now seems to be doing pretty good.
Its as easy as the game looking at the hosts LL and saying they cant restrict above their own (a 370 can't say: 371+). Also Bungie could have a cap. Say the raid is 390, you cant go higher than a 390 cap. (Can't say: must be 391+). Youre limiting yourself. Bungie can be as crteative as needed on this.
Because perception is a double edged sword. The most powerful marketing is word of mouth. Have enough bad experiences and you will talk about how bad a time you're having. Enough people do that and the playerbase evaporates. Also something commonly seen in MMO's which largely do gangbusters on launch and die out if the endgame is too easy, too hard, or bugged to shit.
Think about all the times you've been annoyed at Crucible due to teammates. Now instead of a 10-20 minute activity that you can get a fresh start on again immediately afterward, change that to an hour or more long investment that falls apart and due to lockouts you can't start fresh again until next week. Imagine how much more upsetting that is.
Kill one boss, fail 2 or 3 times (or more) on second boss. 2 people rage quit. Now you have to refill. But who wants to join a partially cleared Raid run?
Player browsing/matchmaking sees/joins a partial clear. Maybe they need replacements because someone had a legit reason to leave but far more likely is that they failed and had quitters. Was it the quitters bringing them down or the people who stayed? No idea. But should I commit my lockout to finding out? Nah. Just run a fresh one instead.
You've also got the "I only want one specific drop from this run" types who have no reason to join if the boss they want is down and no reason to stay once the boss they want killed. Etc... And so on...
All this stuff leads to a ton of players being frustrated and there's nothing a Dev can do to fix this frustration because its source is player interaction. Banning cuts profit potential and risk Dev reputation so it's a last ditch/worst case response.
This stuff is complex and most people never bother to consider the complexities. They don't care. They just want what they want. Give it to them or else. And if they don't like it when they get it, fix that too or else. It's not at all easy to balance this stuff.
How is anything you're saying different than how it is now, except through a 3rd party site/LFG?
Who wants to join a partially cleared raid run? Um... a lot of people. Anyone who has already cleared everything before that checkpoint or anyone who wants to do the later half of the raid.
Was it the quitters bringing them down or the people who stayed? No idea. But should I commit my lockout to finding out? Nah. Just run a fresh one instead. No one gives a shit about this. How many LFG runs have you had on Destiny? If I want to just run final boss, I don't care. I join a CP that is on final boss. Why run an entire fresh raid if you already have the loot from 75% of it or you only want the final boss loot?
You've also got the "I only want one specific drop from this run" types who have no reason to join if the boss they want is down and no reason to stay once the boss they want killed. Etc... And so on... Again, how is this different from LFG? Who cares if someone only want to join at final boss. Or only want to do 1st bos for loot/challenge, then they leave? People already do this in LFG. How is an ingame LFG any different?
Idk man, you just seem to be saying, 'it wont work so dont even try' instead of actually trying to think of ways to make it work. LFG on a 3rd party site works. LFG in game, would therefore work, and be better since its in game.