Im in league 2 and its possibly my favorite game mode. I didnt like it at the start at all, but my perception changed. 

Bots are unbelievable idiots, you can avoid playing with bots if you press cancel at around 32 seconds of waiting, and then start again. This although depends on your region, in UK I rarely have any issues to get 4 players, i noticed the most difficult days are weekends mornings/afternoons.. And if i forget about 32 seconds rule while waiting then the bots are added at about 42 seconds for me. 

Other regions are very different story though, people like NightFury live somewhere around North Pole in a shiny igloo, they can only play with bots, there is purely no choice there.. He says he even prefers it.

And the bots itself is a separate story, i recently played with Deathwalker on my side, i was Salvor and watching my bot engage with enemies, i was giving him healing just about enough for him to keep battling while his ability was still active. What do you think happened next? His ability was active, he is barely alive, enemy right next to him actively smashing his ass, he suddenly starts retreating and ran away from enemies with barely any health while ability still active. Next thing they catch him when ability rans out and he dies :) great logic.. 

Aegises put their shields and coming out of the shields to fight enemies.. Or completely forget about having any ability.

Salvors who either go full mad healing everyone or sometimes for unknown reason dont heal anyone at all even if you right next to him dying. 

Its just torture to play with bots.. 

Matchmaking is not ideal but when everyone is maxed out it doesnt matter too much unless your ally is not playing or if he is using 3 mechs like Ares juggernaut and slingshot. i can understand lancer because its jumping, paragon because it can carry 2*16 weapons.. zypher or guardian because their abilities are very valuable, killshot is realistic.. orion good mech.. etc.. but ideally all legendary mechs should be playing.. with only 1 common/uncommon.. at least use epic. i had aegis forever and it was often killer of both enemies. 

I enjoy HS mode a lot, and in my region there's very little possibility of bots taking over a match. It sometimes happen in off-peak hours (like at midnight or at early morning, some ungodly time to play Mech Arena tbh)

I'm happy to play with bots (only at CPC matches) cuz I can expect the same level of stupidity at both sides (there are exceptions, when opponent bots become crazy smart)

League 1 as endgame as you can imagine.

The most important aspect is your map/weapon knowledge and maximising your odds which thankfully doesn't require P2W hangars like other gamemodes. A blizzfrost, surge, Redox etc. ability can cover almost a third of the smallest map which many players could get Surge for free (Edit: with radius implants).

Bots can be instant losses, which the problem isn't their builds but the variance bewteen a killshot versus an Outlaw with seasonal modifiers.

Overall though it's the only gamemode I play, very rewarding when I play evenly skilled players/content creators.

I have a mixed experience. I have mostly 4-star mechs and a few 5-star mechs, so I have the option of league 3 and league 2. But probably because of my region and play timings, when playing league 2 I'm often at the bottom rung of the league (in terms of stars) while my opponents are often purple star mech players. 

So I downgraded to league 3 and was surprised to see that most players in league 3 are actually similar to me in terms of gear (4 star legendary mechs for the most part). My experience here has been good for the most part. I get totally wrecked many times but I also manage to win a few times, so it's a fun mode for me, and some of the best "I wish I had recorded that" plays happen in this mode (both from my side and my opponents).

Side note: I feel bad that new players with less strong gear, who ideally should have been at league 3, are forced to play in league 4.. just as I am forced to play in league 3 for now. But that's because Plarium changed the star ranges a while ago. Most of the people playing in league 3 these days would be in league 2 in the older system (including me).