How strong are acolytes in 2 Edition? Has anything changed?

They are stronger now than they were in DH1, and tend to start with access to better gear. Not quite RT level, but noticeably a cut above a regular hiver or similar mook.

Yeah, they have definitely got a face-lift in terms of power, especially in the equipment department. They probably won't hold their own until they acquire ~2000xp but unless they try to fight Elite-level opponents alone it won't be a problem either.

Later on there could be problems though. Thankfully to the Aptitudes system, 2.0 Acolytes tend to specialize and rely on the others to do something they can't as out-of-role advancements are many and pretty expensive.

First off, you have 500xp 20+2d10 Acolytes, which are squishier than before, but can have better armor (the Arbites and IG are options to almost everyone). The big issue is XP costs gone up so much (and you will have 1-2 "cheap" stats to advance, compared to the almost guaranteed 3 in DH1e) with the aptitudes system and some aptitudes are plainly better than others. Social affects more talents and skills than Fellowship for example. Tech is almost useless for most folks (barring Techies), yet more than one role gets it.

This is helped a bit by the optional rules of 25+2d10 for most stats and giving out 900xp. This lets them have a chance to do better. Though sadly there is still a XP tax in items like "Low Tech" training so you can use simple melee weapons, being able to speak/read low gothic, as well as a couple basic skills (and parry needs to be bought as well).

You have a greater flexibility overall, but PCs can jump up and grab tier 3 talents with fair ease once a certain amount of XP has been spent, which can be a bit unbalancing in some ways.

Starting Acolytes in DH 2 are considerably stronger than DH 1 Acolytes. IMO this is a good thing; in DH 1, novice Acolytes were embarrassingly incompetent at even tasks that were within their supposed field of expertise. DH 2 Acolytes get more XP and skills, and if the GM allows they have the option to begin with 25+2d10 in their Attributes. Based on my playtesting experiences this is a good change; my DH 1 party repeatedly flubbed the most basic skill tests until they could purchase all their essential skills. A starting DH 2 party feels more like a group of skilled but unexceptional individuals than a rag-tag collection of incompetent murder-hobos, IMO a good beginning for low-ranking Inquisitorial agents.

Character starting gear is also noticeably better than in DH 1, though they are still quite weak compared to characters in other 40k RPG systems. Depending on your character's background, you can begin the game with "tier two" weapons like flamers and chainswords, plus a few free acquisitions that can be spent on nice gear like photo-visors and Guard flak armor. High-end equipment like bolters and power swords are still far out of reach for starting Acolytes though, so they have plenty of room to improve with time. Arbites characters can actually start with their iconic carapace armor and shock maul combination instead of the lame flak jacket and break-action hunting shotgun given to them in DH 1. Again, I feel that this is a good change, and my players started with good enough gear that they haven't been compelled to loot enemies for basic equipment.

Overall, my group and I like the Aptitude system a good deal more than the classes in DH 1. You can theoretically get any skill or talent as long as you meet the prerequisites, though it is more expensive to purchase advances outside your character's Aptitudes. You can gimp your character if you repeatedly take advances that don't match your Aptitudes, but overall we've been pleased with the system. It improves the strength of the party as a whole because Acolytes can take whatever skills the group needs (ex. Medicae, Lore skills). This prevents awkward moments where three Acolytes stand around as their friend dies of Blood Loss because nobody can get Medicae until Rank 5 (this actually happened).

Low-Tech training should just be given to all characters. Otherwise, you're stuck with characters who can use chainswords and shock mauls at character creation but can't use a normal sword or club. IIRC the dev team's reasoning for this was that they didn't want everyone to be proficient with bows and bolas, but I think that's less immersion-breaking than the current issue.