Is it easier to learn L2 that is similar to L1?

Level 1—Coalescence. Two items in the LI become coalesced into one item in the L2.
Level 2—Underdifferentiation. An item in the LI is absent in the L2.
Level 3—Reinterpretation. An item that exists in the native language is given a new shape or distribution.
Level 4—Overdifferentiation. A new item entirely, bearing little if any similarity to the native language item.
Level 5—Split. One item in the native language becomes two or more in the target language.”
Regarding contrastive analysis methodology, several case studies of various language pairs have been conducted to figure out the problems of effective second language acquisition. These studies have shown that both first and second language learners follow a so-called developmental pattern, which is followed in many cases. Rod Ellis (1984) supports the idea of developmental orders in detail and highlights three main stages like “the silent period, formulaic speech, and structural and semantic simplification.” The silent period is described as the period of listening to language and discovering what the language is. In this period learners are not required to produce L2 immediately. The fact is that it is widely accepted in both L1 and L2 acquisition processes. Krashen (1982) supported the silent period that can build competence in the learner via listening while Gibbons (cited in Ellis, 1994) claims that it is a stage of incomprehension.
Formulaic speech is the next developmental stage. It is defined as learning common expressions which can be used on particular occasions (Lyons, cited in Ellis, 1994). Krashen (1982) suggests that these expressions can be used in daily conversations and as Ellis (1994) notes these expressions can consist of entire scripts such as greetings.
The third stage is when learners apply structural and semantic simplifications to their L1.
This process is taking the form of omitting grammatical functions like articles and auxiliary verbs and semantic simplifications happen when omitting content words like nouns and verbs. There are two possible reasons why such simplifications happen. The first reason is that the necessary linguistic forms were not acquired by learners yet. The second reason is that they are not able to use appropriate linguistic forms during the production of L2.
These three stages reveal that L1 and L2 learners go through similar stages of development in the learning process. The linguistic universals were put forward by two well-known SLA linguists Greenberg (in Ellis 1994) and Chomsky. Their studies aimed to identify which features have in common languages that are drawn from different language families. In my research, I would use the theories that they put forward and conclude the experimental study.