The outcry about boosting is a Red Herring

I have never been against players getting full XP in bot lobbies, custom maps, or even custom modes if the XP is somewhat relative to what can be earned in other modes. Just like how the BR is more XP/h than the MP I choose not to play it because I don't enjoy it. The same can be said if someone decides to play against bots I don't really have a problem with increased XP rates within reason and will choose not to play it just like the BR because it's not fun to me.

What is unacceptable is the clear exploits that are granting 100,000+ XP every few minutes. These kinds of farms should not be acceptable in any way shape or form because despite what you think weapon attachments do have a significant impact on gameplay in multiplayer.

Since you are using for your example my speciality I'll take the snipers for example and I'm cursing myself for revealing it but I will. The 6x Thermal and Anti Glare Coating unlocked at 40 (at least on the scout I can't remember for the others) is a literal game changer. It has a significant impact on gameplay to the point where I was going 30+/0 vs 20+/5 in breakthrough on Attackers. You claiming the ADS time lowers the appeal and balances it out is just pure and utter excuses.

 It is not as apparent on other guns but it does show up with increased mag size on smaller capacity SMGs, etc. So saying it has no impact is extremely disenguous.

On top of that it's just purely and utterly demoralizing to a lot of people who do take pride in increasing their overall rank or the rank of a weapon. Someone being able to get a rank 500 scout in 30 hours of exploiting vs the 200-300 it would take me to do it normally ruins every aspect of the longevity and enjoyment I was going to get out of playing this game long term.

The problem you are having is that guns take far too long to level and I do not in the slightest disagree with you 1-50 should be significantly faster, but from what your last few sentences suggest is you feel you should be entitled to the same stuff as someone who put in more hours which is just flat out false. 

You do not deserve the same amount of unlocks as someone who plays longer, do they need to be lowered a tad absolutely, but by no means should you be able to bypass the time investment with a bot lobby. 

TLDR: Normal Bot Lobby's fine with rates relative to other content. Exploit XP Lobby's are not fine remotely full stop. You aren't entitled to everything you want.

Am I proving your point? Sure, but that's because we partially agree with each other and partially disagree. Where we disagree is that you're arguing that people should boost to create an equal playing field as opposed to just legitimately playing the game. That invalidates the reason for there to be a progression system.

Practically speaking, not everyone is going boost. Yet that's exactly what exacerbates the potential gap between players. Players may not progress at the same pace due to time constraints, but that's still a much smaller gap than having a player with few unlocks play against a boosted player who has everything unlocked. Especially if you consider how the progression was much slower in the first few weeks than it is now.