White space is your friend.
Rituals are limited for the same reason spell slots are limited. Those spells are simply not meant to be cast at-will and creating too many ritual tags radically increases the capability of classes. Comprehend languages specifically states "literal" comprehension. Tongues is two-way communication without the "literal" qualifier so would include colloquialisms, for example, based on that distinction.
When you say "only about 17-18" it's 18, and the UA is adding 2 more to bring it up to 20 rituals. How many rituals do you think bards, warlocks, and sorcerers actually have at any given time? I'll answer that.
Sorcerers usually have none.
Warlocks usually have none, some might go with the tome warlock. The tome warlock has an opportunity cost in the invocation but can add rituals from any class. Finding scrolls for bard/cleric/druid is less common and any wizard scrolls found the wizard would have also found. Wizards generally hold the advantage with free rituals gained leveling.
Bards have rituals. The spells known mechanic restricts it significantly to rituals the player really wants and limits the number actually taken. I usually have 4 or 5 rituals on a bard.
When you say "only 18" it's kind of missing the fact that wizards have the best ritual list in the first place, and typically access to the most rituals. There are ways to pay the opportunity costs and add rituals but it's a strong point for the wizard class, and one of the reasons to play a wizard.
I would have more concern regarding item creation guidelines if a group is using them. 1st-level spell scrolls are 25gp and 1 day to craft. Price and time increases drastically but that's also where the bulk of common rituals occurs. For a wizard, that means find a scroll, scribe the scroll, craft the scroll twice and he has twice as many scrolls than he started with. For warlocks, sorcerers, and bards it means suddenly being able to craft a much wider variety of scrolls via spell versatility. It's really only practical for 1st-level spells given the costs and time but a clear advantage coming out of the UA changes. Opinions will probably vary on how important that is. Maybe it'll turn into "Sorcerers and Scroll Cases".
Wizards start with 6 spells. Comparing what a wizard has to what a wizard may or may not have doesn't actually compare the wizard to warlocks, sorcerers, or bards. You're basically arguing one of the reasons to take a wizard isn't a big enough benefit because some of the options are better than others for wizards.
Campaign books with magic purchasing listed or XGtE magic purchasing guidelines helps add things you might not take while leveling up, but even without those options the wizard is going to take the rituals and spell he or she wants while leveling at a minimum. It's not like they would take a poor ritual over a good ritual.
Magic mouth is a good ritual. That's another topic, however.
Contact-other-plane is part of a category of divinations meant to be restrictive. Some spells were given restrictions. This limits them in use and adds "this magic is unreliable or risky" flavors. It's not a unique restriction to wizards.
I usually take 2-3 rituals at 1st level on a wizard in my book. I might take magic mouth at 4th level. 5th level has a lot of competition for spells and rituals, and I'm likely to take another ritual at 6th level. Half a dozen or more rituals by 10th level is very easy.
"I wish I had more stuff" isn't a wizard only issue by any means. The problem with that argument is wizards have more than those other classes. When someone is playing a sorcerer it's not like they are going to have acid arrow, vampiric touch, and faithful hound all known either walking into the same scenario the wizard does. It's not like they are about to stop an encounter to change spells.
Caveats: ASI's are assumed to clerics, druids, and wizards asap; many would take a feat and delay 1 spell prepped from levels 4 to 11 or levels 8 to 11. Domains are included for clerics and paladins. Arcanum is included for warlocks and invocations are not. Paladins have a straight 16 CHA assumption; adjust as appropriate to your expectations. Rangers are including the changes in UA class variants; we're keeping on topic here.
Any time you think "I wish I had so-and-so spell prepped" will happen less often than "I wish I knew so-and-so spell" on a warlock or sorcerer. Bards do have a solid spell list and know a lot of spells in comparison but lack in other areas that I went over in the bard thread. Spells known isn't the whole story (spell lists matter a lot) as well. The cleric for example is much less likely to not have a cleric spell prepped he or she wants but he's still never going to have spells on the wizard list he or she wants. IE different classes are different.
The only reasons I play sorcerers are flavor and meta-magic. I like meta-magic and can make the spells known work well enough. Spell versatility isn't going to change that. It's going to make the limited spells known a little less painful in the process. The reasons I play warlocks are for flavor and invocations. Their spell mechanics gives the spells known spread over a smaller level range while invocations are a huge part of the class so spell versatility looks like it's barely a noticeable benefit on that class, tbh. I play bards for flavor and versatility. They have a good spell list but they can't actually cast spells as effectively as other arcane spell casters. Spell versatility isn't going to change that but it does look like a person can respec an easy-to-tailor class and retailor it as needed given sufficient downtime.
Spell scribing is a bonus. The class was designed with that expectation. The rarity or duplication of spells that are found when it's a bonus doesn't turn that bonus into a drawback. That's how magic items are treated in 5e as well.
Probably ROFL because it take the sorcerer an entire day to figure out how to open a door.
That implies spell versatility is the equivalent of spell preparation, which it isn't. A more apt comparison would be giving fighters spells, which would be the eldritch knight compared to a wizard.
Or it's just good as is and different.
Wizards have very definite advantages. They have a strong spell list, spells prepped is more available spells than spells known at any given time, class and subclass abilities make their spellcasting better, other ritual caster classes need to prep or learn rituals while wizards have a strong ritual list that they specifically don't have to prep (which moves them closer to clerics than druids in my chart earlier because of it).
Swapping out spells is one of the least important reasons to play any of these classes. That should be clear because most people only make minor spell swaps if they make them at all with prep classes. Spell versatility mostly only validates spells on spell lists that spells known classes cannot afford to ever take because those spells are too situational.
Players are still going to play sorcerers for meta-magic and warlocks for eldritch blast or one of the subclasses the like. They aren't going to look at those spell lists and think "I gotta get me some of that spell swapping no where near what a prep class can do" instead of just taking a prep class.
